I3C was first mentioned on Feb. 19 Jolla Phone update - Lights on, technical bits and the schedule when batch #3 was in the 9000s.
The phones being shipped right now are also from late batch #3 and finally have I3C.
I would say it is very likely that all who have seen “I3C” as specification at the time of pre-order are actually getting a phone with an I3C board.