But I had a comment from Suzanne, which seems to resolve the issue for me. She said:
Which end you thread from has to do with which direction the twist is in the thread. You want the thread to travel in the direction of twist. BUT you don't have to get all technical and microscopic about it - there's an easy test.
Holding on to one end of the thread, take it between the nails of the thumb and forefinger of the other hand and quickly run down the thread - sort of "stripping" it. If it bunches up - thread from the bottom end, if the thread stays straight, thread from the end you are holding. If you observed which was the spool end - so much the better.
Thank you Suzanne!
Actual poll results: