Wow! Finally made it to the end - got the theme from the extra column, but it took me a while to get the final pdm on the two unclued entries and the link back to the titular theme. now that is all there, I have to say I'm amazed at the construction.
A few of the clues were simply wonderful too - particularly 7, 8 and 9.
Have a few wordplays/definitions still to resolve satisfactorily to say that I've really completed it (H, L, R, T, 6, 10, 11, 13, 15) but those can wait until tomorrow!