score:1
https://tankarchives.blogspot.com/2017/05/pzkpfw38t-prize-from-bohemia.html
mentions that the 38t from the second production batch had 4 crew members, the first (much smaller) batch, in part vehicles repurposed from a canceled Czech order, had 3.
This change seems to have been made pretty early in production, effectively after what we'd now call operational acceptance trials.
This and several other design changes were made in June 1939.