I really like the Re4 HT Leon's hair and face! And also, wasnt it Wesker who saved Ada after her fall from the railings near the end of the A mission in Re2? And also Brad Vickers and Barry Burton were both in Nemesis (And Brad was Also in Re2 but reanimated as that portion of Re2 was After his living and being killed moment by Nemesis in the 3rd).
So maybe Chris was still kicking around somewhere too but as of yet he has not been giving a whereabouts for the events. His desk in the STARS office of the RPD station had been left looking a mess before it gets investigated by Jill, Leon and Claire in Re2-3 so maybe he had been back to the station to get something in a hurry!