I appear to have completed this without understanding the last part of the preamble:
'...identifies which letter solvers should choose in two cells with clashing entries.'
I think I can identify one clash but don't see how it relates to the bottom layer of the construction created by the end game.
Also, 2 parses are evading me. 18a Defied editor...
6d Same Scottish...
For 6d I can see 'same Scottish'- 2 letters + line but then?
18a I have 5 crossing letters and can see the usual editor but 'nothing at end of letter'??