Solution
Pascal Wassong (version by Gerd Wilts) Dedicated to Babette
14+12. Last 55 single moves?
The last moves were: -1. .. Bb8-a7 -2. Qa3-a2 f4-f3 -3. Ra2-b2 Qb2-c1 -4. Rc1-b1 Qb1-b2 -5. Rb2-a2 Qa2-b1 -6. Rb1-b2 Qb2-a2 -7. Qa2-a3 Qa3-b2 -8. Rb2-b1 f5-f4 -9. Qb1-a2 Qa2-a3 -10. h7-h8=B Qa3-a2 -11. Ra2-b2 Qb2-a3 -12. Ra3-a2 Qa2-b2 -13. h6-h7 Qb2-a2 -14. Qa2-b1 Qb1-b2 -15. h5-h6 Qb2-b1 -16. Rb1-c1 Qc1-b2 -17. Rb2-b1 Qb1-c1 -18. h4-h5 Qc1-b1 -19. Qb1-a2 f6-f5 -20. Ra2-b2 Qb2-c1 -21. Qc1-b1 Qb1-b2 -22. Rb2-a2 Qa2-b1 -23. Rb1-b2 Qb2-a2 -24. Ra2-a3 Qa3-b2 -25. Rb2-a2 a2-a1=N -26. Ra1-b1 f7-f6 -27. Rb1-b2 Qb2-a3 -28. h3-h4 (not h2-h4!) a3-a2 -29. a2xBb3 (this is no longer unique, since -29. Ra2-a1 Qa1-b2 -30. Rb2-b1 Qb1-a1 -31. Ra1-a2 Qa2-b1 -32. Rb1-b2 Qb2-a2 could've happened too) Bc4-b3 -30. b3xNa4 Nb6-a4 -31. h2-h3 (this tempo is needed, so retracting h3-h4 earlier is necessary!) Ba7-b8 -32. Nb8-a6 Bb5-c4 -33. Na6-b8 a4-a3 -34. Nb8-a6 a5-a4 -35. Na6-b8 Qa3-b2 -36. Nb8-a6 Qa4-a3 -37. Qa3-c1 a6-a5 -38. Rc1-b1 Qa5-a4 -39. Qa4-a3 Kb2-c3 and finally the position is unlocked.
This problem is a version of the following problem:
Pascal Wassong Europe Echecs Jan. 1994 Dedicated to Babette
14+12. Who mates in one?
which has the same solution as the first problem, apart from the first two moves.