As I commented in my PM to Børge, I found A199 V1.75 a challenging and interesting puzzle so thanks for posting it. While the key area was the same as for A199 the solving techniques used were different.
Here is my walkthrough for A199 V1.75. I've had another look at step 20b and found that my original eliminations were correct but I hadn't explained one clearly; I hope it's better now. I've also corrected a few typos.
40(8) cage at R1C9, 18(4) cage at R1C2, 21(4) cage at R2C1, 24(4) cage at R2C9 and 22(4) cage at R9C2 are disjoint cages. I hope that people won’t be confused by my use of the term “disjoint cages”; they are more commonly called “remote cages” but I find that “disjoint” is a better description.
Prelims
a) 7(3) cage at R1C5 = {124}
b) 11(3) cage at R3C2 = {128/137/146/236/245}, no 9
c) 19(3) cage at R6C1 = {289/379/469/478/568}, no 1
d) 11(3) cage at R6C5 = {128/137/146/236/245}, no 9
e) 22(3) cage at R7C5 = {589/679}
f) 10(3) cage at R8C3 = {127/136/145/235}, no 8,9
g) 40(8) disjoint cage at R1C9 = {12346789}, no 5
Steps resulting from Prelims
1a. Naked triple {124} in 7(3) cage at R1C5, locked for C5 and N2
1b. 22(3) cage at R7C5 = {589/679}, 9 locked for C5 and N8
[Now for the obvious move seen in less than 3 seconds.]
2. R5C5 = 5 (hidden single on D/), clean-up: no 8 in 22(3) cage at R7C5 (step 1b)
[Alternatively 45 rule on D/ 1 innie R5C5 = 5, ...
I’ve omitted my usual “placed on diagonal” statements because they are placements within the 40(8) and 45(9) cages.]
3. Naked triple {679} in 22(3) cage at R7C5, locked for C5 and N8
3a. Naked pair {38} in R46C5, locked for N5
4. 11(3) cage at R6C5 = {128} (cannot be {245} because R6C5 only contains 3,8) -> R6C5 = 8, R7C46 = {12}, locked for R7 and N8
5. R4C5 = 3 (naked single), R3C46 = 13 = {58/67}, no 9
6. 45 rule on N8 2 remaining outies R8C37 = 7 = {16/25/34}, no 7,8,9
7. 10(3) cage at R8C3 = {145/235} (cannot be {136} because 1,6 only in R8C3) -> R8C3 = {12}, 5 locked for C4 and N8, clean-up: R8C7 = {56} (step 6), no 8 in R3C6 (step 5)
8. 8 in N8 only in R89C6, locked for C6
9. 45 rule on N2 2 remaining outies R2C37 = 5 = {14/23}
10. 45 rule on R5 2 remaining innies R5C46 = 11 = {29/47}, no 1,6
11. 14(3) cage at R1C4 = {167/239/347} (cannot be {149/248} because 1,2,4 only in R1C4), no 8
11a. 2,4 of {239/347} must be in R2C3 -> no 3 in R2C3, clean-up: no 2 in R2C7 (step 9)
12. R3C4 = 8 (hidden single in C4), R3C6 = 5 (step 5)
13. 14(3) cage at R5C1 = {167/239/347} (cannot be {149/248} which clash with R5C46), no 8
14. 8 in R5 only in 15(3) cage at R5C7, locked for N6
14a. 15(3) cage = {168/348}, no 2,7,9
15. 18(3) cage at R4C7 = {279/459} (cannot be {369} which clashes with 15(3) cage at R5C7, cannot be {567} which clashes with R8C7), no 1,3,6
16. 3,5 in C4 only in R1289C4 -> R1289C4 = {37}{45}/{39}{45}/{67}{35} (only combinations for R12C4 consistent with 14(3) cage at R1C4 ) = 19,21
16a. Combined cage 14(3) cage at R1C4 + 10(3) cage at R8C3 = 24, R1289C4 = 19,21 -> R28C3 = 3,5 = {12/14}, 1 locked for C3
17. 11(3) cage at R3C2 = {128/137/146/236/245}
17a. 3 of {137} must be in R3C2 -> no 7 in R3C2
18. 19(3) cage at R6C1 = {289/379/469/478/568}
18a. 3 of {379} must be in R6C12 (R6C12 cannot be {79} which clashes with 14(3) cage at R5C1) -> no 3 in R7C2
19. 16(3) cage at R4C3 = {259/268/349/457} (cannot be {358} because no 3,5,8 in R5C4, cannot be {367} which clashes with 14(3) cage at R5C1)
19a. 8 of {268} must be in R4C3 -> no 6 in R4C3
20. 45 rule on N4 3(2+1) outies R37C2 + R5C4 = 15
20a. 8 in R4 only in 11(3) cage at R3C2 or 16(3) cage at R4C3 -> 11(3) cage at R3C2 = {128} or 16(3) cage at R4C3 = {268} = [826]
20b. 11(3) cage at R3C2 (step 17) = {128/146/245} (cannot be {236} which clashes with 16(3) cage = [826], cannot be {137} because R3C2 = 3, R5C4 = 2 from 14(3) cage = [826] so R37C2 + R5C4 cannot total 15), no 3,7
20c. 6 of {146} must be in R3C2 (R4C12 cannot be {16/46} which clash with 16(3) cage = [826]), no 6 in R4C12
20d. 11(3) cage at R3C2 = {128} or 16(3) cage at R4C3 = {268}, CPE no 2 in R5C2
[When I checked my walkthrough, I thought that I’d made an error in step 20b. However on more careful examination I found that it was correct but I hadn’t explained it clearly.]21. R37C2 + R5C4 = 15 (step 20)
21a. R3C2 + R5C4 cannot total 7 -> no 8 in R7C2
22. 19(3) cage at R6C1 = {379/469}, no 2,5
22a. 19(3) cage = {379/469}, CPE no 9 in R5C2
22b. 7 of {379} must be in R7C2 (R6C12 cannot be {37} which clashes with 14(3) cage at R5C1), no 7 in R6C12
Re-work step 23 deleted.24. 7 in N4 only in 14(3) cage at R5C1 (step 13) = {167/347} or 16(3) cage at R4C3 (step 19) = {457} with 7 in R46C3, CPE no 7 in R5C4, clean-up: no 4 in R5C6 (step 10)
24a. 16(3) cage at R4C3 (step 19) = {259/268/349/457}
24b. 3 of {349} must be in R6C3, 4 of {457} must be in R5C4 -> no 4 in R6C3
25. R37C2 + R5C4 = 15 (step 20)
25a. R5C4 + R7C2 cannot total 14 -> no 1 in R3C2
25b. R3C2 + R5C4 cannot total 9 -> no 6 in R7C2
26. 11(3) cage at R3C2 (step 20b) = {128/146/245}
26a. 11(3) cage at R3C2 = {128} or 16(3) cage at R4C3 = {268} (step 20d) = [826], 6 locked for N4 => 14(3) cage at R5C1 (step 13) = {239/347} => 1 in N4 only in R4C12
-> 1 in N4 only in R4C12, locked for R4 and N4
26b. 11(3) cage at R3C2 = {128/146}, no 5
26c. 2 of {128} must be in R3C2 -> no 2 in R4C12
26d. 2,6 only in R3C2 -> R3C2 = {26}
27. 1 in R5 only in 15(3) cage at R5C7, locked for N6
27a. 15(3) cage (step 14a) = {168} (only remaining combination), 6 locked for R5 and N6
28. 3 in R5 only in 14(3) cage at R5C1, locked for N4
28a. 19(3) cage at R6C1 (step 22a) = {469} (only remaining combination), no 7, 6 locked for R6, CPE no 4 in R5C2
29. R37C2 + R5C4 = 15 (step 20) = [249/294] (only remaining permutations) -> R3C2 = 2, R5C4 = {49}, clean-up: no 3 in R2C7 (step 9), no 9 in R5C6 (step 10)
30. R3C2 = 2 -> 11(3) cage at R3C2 (step 23b) = {128} (only remaining combination), 8 locked for N4
31. Naked pair {14} in R2C37, locked for R2 -> R2C5 = 2
32. 14(3) cage at R1C4 (step 11) = {167/347}, no 9, 7 locked for C4 and N2
32a. 16(3) cage at R1C6 = {169/349}, 9 locked for C6
33. 5 in N4 only in R46C3, locked for C3
33a. 16(3) cage at R4C3 (step 19) = {259/457}
33b. R5C4 = {49} -> no 4,9 in R46C3
34. 18(3) cage at R4C7 (step 15) = {279} (only remaining combination, cannot be {459} because R5C6 only contains 2,7), 9 locked for C7 and N6
35. 14(3) cage at R3C8 = {257/347} (cannot be {149/167/239/356} because 1,3,6,9 only in R3C8), no 1,6,9
35a. 14(3) cage = {257/347}, CPE no 7 in R6C8
35b. 3 of {347} must be in R3C8 -> no 4 in R3C8
36. 3 in N6 only in R6C89, locked for 15(3) cage at R6C8, no 3 in R7C8
36a. 15(3) cage = {348/357}, no 2,6,9
36b. 8 of {348} must be in R7C8 -> no 4 in R7C8
37. 45 rule on N6 3(2+1) outies R3C8 + R5C6 + R7C8 = 17 = [377/728], no 5, 7 locked for C8
37a. 15(3) cage at R6C8 (step 36a) = {348/357}
37b. R7C8 = {78} -> no 7 in R6C9
38. 14(3) cage at R3C8 (step 35) = {257/347}, CPE no 7 in R123C9
38a. 4 of {347} must be in R4C8 -> no 4 in R4C9
39. 7 in C8 only in R37C8, 7 in 14(3) cage at R3C8 only in R3C8 + R4C9
R7C8 = 7 or R3C8 = 7 => no 7 in R4C9 => 7 in N6 only in R46C7
-> R7C8 = 7 or R46C7 must contain 7, CPE no 7 in R79C7
40. 18(3) cage at R4C7 = {279} (step 34)
40a. Consider placement for 7 in C6
R4C6 = 7
or R5C6 = 7 => R4C9 = 7 (hidden single in N6)
or R6C6 = 7 => R4C7 = 7 (hidden single in 18(3) cage at R4C7)
-> 7 locked in R4C679, locked for R4
41. 14(3) cage at R3C8 (step 35) = {347} (only remaining combination, cannot be {257} which clashes with R4C3) -> R3C8 = 3, R4C89 = [47], R6C89 = [53], R7C8 = 7 (step 36a)
42. Naked pair {29} in R46C7, locked for C7 and 18(3) cage at R4C7 -> R5C6 = 7, R5C4 = 4 (step 10)
43. R5C2 = 3, R5C13 = {29}, locked for N4 -> R46C3 = [57]
44. Naked pair {46} in R6C12, locked 19(3) cage at R6C1 -> R7C2 = 9, R7C5 = 6
45. Naked pair {35} in R89C4, locked for C4 and N8, R8C3 = 2 (step 7), R8C7 = 5 (step 6), R5C13 = [29], R89C4 = [35]
46. R2C3 = 1 (hidden single in C3), R2C7 = 4
47. Naked pair {67} in R12C4, locked for C4 and N2
48. R4C6 = 6 (hidden single in C6)
49. R7C1 = 5 (hidden single in R7)
49a. 21(4) disjoint cage at R2C1 = {1569/3459/3567} (cannot be {1578} which clashes with R4C1), no 8
49b. 3 of {3567} must be in R2C1 -> no 7 in R2C1
49c. 4 of {3459} must be in R8C1 -> no 4 in R3C1
49d. Killer pair 4,6 in 21(4) disjoint cage and R6C1, locked for C1
50. 3 on D/ only in R7C3 + R9C1, locked for N7
51. R2C9 = 5 (hidden single in R2)
51a. 24(4) disjoint cage at R2C9 = {4569} (only remaining combination) -> R7C9 = 4, R38C9 = {69}, locked for C9
52. R1C2 = 5 (hidden single in R1)
52a. 18(4) disjoint cage at R1C2 = {2358/2457} (cannot be {1359} which clashes with R1C6, cannot be {1458} which clashes with R1C5, cannot be {3456} because 3,4 only in R1C3) -> R1C8 = 2, R1C3 = {34}, R1C7 = {78}
53. R3C9 = 6 (hidden single in N3)
and the rest is naked singles.