After seemingly completing about 85% of the grid I've just realised that in my foolishness I misinterpreted the preamble, taking it to mean there was one instance of one letter dropped down to the bottom row per column, rather than each instance of that letter. As a result I've realised that my 10th column is impossible as filled, as the dropped letter still appears elsewhere in the column. I'm not sure how to tackle this, given I was pretty confident about the wordplay in the relevant 17d and I don't see any way to fulfil the preamble with what I have.
Would someone sanity-check what I have for a couple relevant clues?
17d. Time to withdraw from reserved holiday destination? (6)
For this I have an answer with 7 letters referring to a generic example of what is defined by the end of the clue (the wordplay works tidily), with the third letter dropped down.
38ac. German philosopher's hesitance about housing unknown national (11)
I have an answer here based on the beginning of the clue, essentially an adjective constructed from a proper noun. To be honest I don't really know how the wordplay works, this was just the only answer I could think of that fit an appropriate definition.
At least something about this must be wrong, because as is, the dropped letter from 17d conflicts with what's in that column for 38ac.