I took the time to have a closer look at the list posted by mith on March 21st. (
the-hardest-sudokus-new-thread-t6539-1230.html#p318907)
It reminds me of a list I made in september 2021. I wanted to know if in ph_2010, all puzzles with equivalent solutions were 'closely' related.
This list was the result of the analysis of all 11.2+ puzzles in ph_2010. It contains groups of puzzles with equivalent solutions. Only groups with at least two members are listed.
The largest group (of puzzles with SER >= 11.2 and equivalent solutions) counted 523 members, all closely related.
The first line of each group is the canonical morph of the common (equivalent) solution of all members of the group.
column 2: line number in ph_2010
col. 3: ID
col. 4: first digits of original puzzle
col. 5: additional puzzle data (unfortunately, on my screen this column goes to a new line)
This is the top of the list (first 7 groups): 
- Code: Select all
- 987654321653921874214873695832495716791368452546712938428137569365289147179546283
 9.....3....3..1.7....8....5.....5.1..9..6.4.....7....842...7....6.2...4...9.4.2..   3   2      12..3....4....1.2...   11.90;11.90;11.30;elev;second flush;2;23;
 9.....3....3..1.74...8....5.....5.1..9..6.4.....7....842...7....6.2.......9.4.2..   33092   39354      98.7..6..5...4......   11.20;1.20;1.20;GP;12_07;39354;23;
 987654321653921874241783956829536417715492638364178295572869143438217569196345782
 .8.6...2.....2...42....39..8..5...1..15.......6..7.........9..3..82...6.....4.7..   5   4      .2.4...8.....8...68.   11.90;11.90;9.90;elev;3;4;22;
 .8.6...2.........42....39..8..5...1..15.......6..7........69..3..82...6.....4.7..   6406   910      .2.4...8.........68.   11.30;11.30;9.30;elev;721;910;22;
 987654321654321987321987654896135472735248196142796835519473268473862519268519743
 9.......1..43...8..2....6......35.7...5..8....4.7......1....2..4...6...9..85...4.   12   7      1.......9..67...2..8   11.80;11.80;11.60;elev;15;7;22;
 9.......1..43...8..2....6......35.7.7.5.48......7......1....2..4...6...9..85...4.   19553   15522      98.76....75....6....   11.20;11.20;11.10;GP;kz1a;15522;23;
 987654321653921874124783659849362715762815943531497268476139582315278496298546137
 ......3..6....1.7..2.7....9..9...7.57...1..4..3....2..4..1...8...5..8.......46...   15   11      98.7.....6...5......   11.80;11.80;11.40;GP;H1;11;22;
 ......3..6....1.7..2.78...9..9.....57...1..4..3....2..4..1...8...5..8.......46...   2261   423      98.7..6....5.9..4...   11.40;11.40;2.60;GP;H72;423;22;
 ......3..6....1.7..2.7....9..9.6...57...1..4..3....2..4..1...8...5..8.......46...   3276   529      98.7.....6.....97...   11.40;1.20;1.20;GP;H86;529;22;
 ..76..3..6....1.7..2.7....9..9.....57...1..4..3....2..4..1...8...5..8.......4...7   13504   15710      98.7.......7.6......   11.30;1.20;1.20;GP;Kz1 b;15710;23;
 ..76..3..6....1....2.7....9..9...7.57...1..4..3....2..4..1...8...5..8.......4...7   13649   18770      98.7.....6...5.9....   11.30;1.20;1.20;GP;KZ1C;18770;23;
 ..76..3..6....1.7..2.7....9..9.6...57...1..4..3....2..4..1...8...5..8.......4....   20400   18307      98.7.......7.6......   11.20;11.20;10.60;GP;KZ1C;18307;23;
 ......3..6....1.7..2.7....9..9.....57...1..4..3....2..4..1...8...5..8.......46..7   38715   3312      98.7.....6.....7....   11.20;1.20;1.20;GP;H654;3312;22;
 987654321653921874124873695875346219496512738312789546748295163569137482231468957
 ..7.5....6....1....2.8...9....3....9.9.....38......54..4.2....35....7.....1.6....   17   12      1.......2..94...5..6   11.80;11.80;11.20;tax;gsf-2007-05-24-003 64879;12;21;
 ..7.5....6....1....2.8...9....3..2.9.9.....38......5...4.2....35....7.....1.6....   80   100058      98.7.....7.6...8....   11.70;11.70;11.20;GP;12_11;100058;21;
 ..7.5....6....1....2.8...9....3..2.9.9.....38......54..4.2....35....7.....1.6....   1708   3269155      .......12.....34.5..   11.40;11.40;11.20;MITH;2020_10;3269155;22;
 987654321653921874214873965869145237375269148142387659728516493531492786496738512
 .8.6...2......1..4....7.9......4...7.....91....23...5..285......3.....8.4.6......   18   13      6.......2.9.4...5...   11.80;11.80;11.10;tax;coloin-04-10;13;21;
 .8.6...2......1..4....7.9......4...7.....91....23...5...85....353.....8.4.6......   21188   287382      .......12.....3..4..   11.20;11.20;10.40;dob;12_12_03;287382;22;*
 987654321654321987312978564876192453245763198193845276731289645528436719469517832
 .8.....2....3...87......5.4..6.9.....4.7....81....5....3.2...4.5....6.....9.1....   19   14      1.......2.9.4...5...   11.80;11.80;10.80;tax;coloin-04-10;14;21;
 .8....32....3...87......5....6.9.....4.7....81....5....3.2...4.5....6.....9.1....   77   39      1.......2.9.4...5...   11.70;11.70;11.20;tax;coloin-04-10;39;21;
It appears that in the overwhelming majority of groups, the members are closely related.
One of the very rare exceptions is the first member of this group:
- Code: Select all
- 987654321654321987312897456865139274723465819491278563546783192238916745179542638
 .8...4.2.6.4.2..87......4..86..3.2.4.2..6.8....1..8..35....3......9......7..4.6..   34734   1886884      98.76.5..7..8..9....   11.20;1.20;1.20;GP;2011_12;1886884;26;
 .8.6.432.6...2..8.........6.6..3...47....5.....1.......4..8...22.89..7...7..426..   39599   1834996      98.76.5..5....9.7...   11.20;1.20;1.20;GP;2016_04_23;1834996;26;
 .8.6.432.....2..8.........6.6..3...47....5.....1.......46.8...22.89..7...7..426..   39609   1834952      98.76.5..5....9.....   11.20;1.20;1.20;GP;2016_04_23;1834952;26;
And now something completely different.
My script for finding new hard puzzles stopped yesterday when skfr did not return a rating result for this puzzle:
..2.3...4...2.53.15..14.8..987......6...........85.....4.3.251....58.4.2....14.8.
I use this command line (in VBA script) for skfr:
res = Wshshell.Run("skfr_win64_v2_0_1.exe", vbHide, True)
However, SER returns this result for the same puzzle:
..2.3...4...2.53.15..14.8..987......6...........85.....4.3.251....58.4.2....14.8. ED=11.0/1.2/1.2