What are the shortest possible games with a) 20 Bishops, b) 20 Knights, and c) 20 Rooks?

Question

The 18 queeens chess problem has already been brought up one CSE: Shortest possible game with 18 queens?

That is a game where all 16 pawns are promoted to queens. But nobody has asked this yet: What are the shortest possible games with a) 20 Bishops, b) 20 Knights, and c) 20 Rooks?

I give below my own attempts. Credit to @Laska for their answer here, as I used some of their games.

 [Title "20 Bishops-104 Half-Moves"]
 [FEN ""]

1. g4 h5 2. g5 Rh6 3. gxh6 g5 4. h4 g4 5. b4 e5 6. f4 e4 7. Nf3 exf3 8. e4 f5 9. e5 Qg5 10. Nc3 a5 11. Ne4 fxe4 12. c4 a4 13.Qb3 axb3 14. a4 b5 15. a5 d5 16. c5 Ra6 17. hxg5 Rd6 18. cxd6 c5 19. Ra4 c4 20. d4 Na6 21. Be3 Nc5 22. dxc5 bxa4 23. g6 g3 24. h7 h4 25. g7 h3 26. b5 g2 27. Kf2 Kf7 28. f5 c3 29. f6 Kg6 30. Kg3 gxh1=B 31. a6 a3 32. a7 a2 33. b6 b2 34. b7 c2 35. c6 d4 36. c7 f2 37. Ba6 f1=B 38. Bf2 e3 39. a8=B Bhg2 40. b8=B h2 41. hxg8=B d3 42. Bb3 d2 43. g8=B Bh6 44. f7 e2 45. d7 a1=B 46. f8=B b1=B 47. d8=B Be6 48. c8=B Bf7 49. e6 c1=B 50. e7 d1=B 51. e8=B e1=B 52. Ba2 h1=B

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[Title "20 Knights-104 Half-Moves"]
[FEN ""]

1. d4 c5 2. f4 e5 3. f5 d5 4. Bf4 Be6 5. fxe6 exf4 6. e4 f5 7. e5 c4 8. Bd3 Bc5 9. dxc5 cxd3 10. c4 a5 11. b4 a4 12. Qb3 axb3 13. a4 b5 14. a5 h5 15. g4 Rh6 16. g5 d4 17. gxh6 g5 18. h4 g4 19. Ra4 Qg5 20. hxg5 bxa4 21. Kf2 d2 22. e7 f3 23. g6 d3 24. g7 Kf7 25. Ke3 Kg6 26. Kd4 f4 27. e6 h4 28. h7 b2 29. a6 a3 30. b5 a2 31. b6 f2 32. c6 f3 33. c7 g3 34. a7 g2 35. b7 h3 36. c5 h2 37. c6 Kf5 38. Nh3 Na6 39. Na3 Nh6 40. bxa8=N gxh1=N 41. c8=N d1=N 42. e8=N f1=N 43. g8=N b1=N 44. h8=N a1=N 45. c7 d2 46. e7 f2 47. Nef6 Nb2 48. Ncb6 Nfg3 49. c8=N f1=N 50. e8=N d1=N 51. Nac7 Nhf2 52. a8=N h1=N

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[Title "20 Rooks-104 Half-Moves"]
[FEN ""]

  1. b4 d5 2. g4 e5 3. h4 f5 4. a4 c5 5. c4 d4 6. f4 e4 7. Nf3 exf3 8. Nc3 dxc3 9. d4 a5 10. e4 h5 11. b5 Na6 12. g5 Nh6 13. bxa6 b5 14. gxh6 g5 15. d5 b4 16. e5 g4 17. Bd3 Bd7 18. Be4 Bb5 19. Qd4 Qg5 20. axb5 fxe4 21. hxg5 cxd4 22.g6 h4 23.g7 h3 24.f5 g3 25.f6 g2 26.Kf2 Kf7 27.Kg3 Kg6 28.Rh2 Rh7 29.g8=R+ Rg7 30.h7 g1=R+ 31.Rg2 h2 32.f7 f2 33.e6 e3 34.e7 e2 35.exf8=R h1=R 36.Re8 f1=R 37.f8=R e1=R 38.h8=R b3 39.b6 b2 40.b7 Ra7 41.Ra2 bxc1=R 42.b8=R Rb1 43.Rab2 Rb7 44. a7 d3 45.d6 d2 46.c5 c2 47.c6 a4 48.c7 a3 49.d7 a2 50.a8=R a1=R 51.c8=R c1=R 52.d8=R d1=R. 

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Answer 1

With many thanks to Remellion suggesting in the comments that finding the fastest ways to get to 16 pawns isn't the best idea, and instead promoting one or two pawns at a time is better, I have found a slightly faster way to get to 20 knights. Thanks Remellion!

The 20 rooks and 20 bishops games are still a work-in progress.

This new 20 knights game is faster by two ply.

[Title "20 Knights-102 Ply"]
[FEN ""]

1. h4 a5 2. h5 a4 3. b4 g5 4. h6 a3 5. Bb2 Bg7 6. hxg7 axb2 7. a4 h5 8. Rh4 Ra5 9. bxa5 gxh4 10. g4 b5 11. g5 b4 12. g6 b3 13. c4 f5 14. c5 f4 15. c6 f3 16. Bg2 Bb7 17. cxb7 fxg2 18. gxh8=N bxa1=N 19. f4 c5 20. f5 c4 21. f6 c3 22. g7 b2 23. a6 h3 24. a7 h2 25. a8=N h1=N 26. a5 h4 27. a6 h3 28. a7 h2 29. e4 d5 30. Ke2 Kd7 31. Kf3 Kc6 32. Kg4 Kb5 33. f7 c2 34. f8=N c1=N 35. Qf3 Qb6 36. d4 e5 37. Qf4 Qc5 38. dxc5 exf4 39. c6 f3 40. c7 f2 41. e5 d4 42. e6 d3 43. e7 d2 44. e8=N d1=N 45. c8=N f1=N 46. Nd2 Ne7 47. Ne2 Nd7 48. b8=N g1=N 49. g8=N b1=N 50. Nab6 Nhg3 51. a8=N h1=N

Note: While these games don't have the need to be symmetrical, it just generally seems to work sometimes.