The expanded form database started from singles expansions of minimals - however, the correct way to read "singles-expanded form" in the current database is "singles expanded from a depth 3 puzzle, which may or may not be minimal".
This is due to the depth_adder script, which takes a given expanded form and tries every possible digit addition, checking for depth. If the depth is still 3, this new puzzle is (after singles expansion, if applicable) added to the database, but there is no guarantee that it is reachable from a minimal by singles.
If you'll recall Loki, its expanded form is 29c; however, when you applied T&E(2), you ended up with a pencilmark grid having 31 digits filled. This 31c is the "max-expand" of Loki - it is in depth 3, but no more digits can be added without reducing the depth. However, none of its four minimals single expand back up to the 31c.
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solution_minlex of expanded forms in the Loki family:
1.3.56....571.9...69.37......1.93..75.96.73.....51.......96..........4....5...86. (Loki and a 27c singles-expand to this 29c)
1.3.56....571.9.3.69.37......1.93..75.96.73.....51.......96..........4....5...86. (a 26c and a 27c singles-expand to this 30c)
1.3.56....571.9...69.37......1.93..75.96.73.....51.......96..........4..9.5...86. (no minimals singles-expand to this 30c)
1.3.56....571.9.3.69.37......1.93..75.96.73.....51.......96..........4..9.5...86. (max-expand 31, no minimals singles-expand to it)
The full "tree" (not really a tree in the graph theoretical sense) for this family would look like:
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31c
/ \
30c 30c
\ /
29c
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As progress on mapping out these trees and finding the min-expands, I have added the full solution grid in canonical form to the database. There are currently 14155 solution grids. 471 of these only have one expanded form associated with them (so these are necessarily both min-expand and max-expand). The most expanded forms for one solution grid is 905.
Obviously there will be a lot more min-expands than distinct solution grids, but there will also be more max-expands. Just taking that 905 as an example, there are two 37c puzzles associated with it:
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.234.678.4.6......78..2346..3..48..664.2.7..88..63.....7....65..6....912....628.7
.234.678.4.6......78..2346..3..48..664.2.7..88..63....37....65..6....91.....628.7
It is possible that there will be some max-expands like this where we can add one of two digits to an existing puzzle but not both without lowering the depth. However, this one is a case of two distinct trees, despite the huge overlap - the 36c intersection of these is not unique! (The 38c union solves with one x-wing and singles.)