In-game files as well as Resident Evil related material state that the Tyrant T-103 was created after Umbrella recovered the research data from the original fight against the Tyrant in Resident Evil. Among the Tyrant T-103 specimens is IVAN, Sergei's bodyguard. The problem is that IVAN appears and fights Wesker in-between the events of Resident Evil 0 and Resident Evil which was about one day earlier than Jill or Chris fought the original Tyrant meaning IVAN would not be created for about two months as the necessary data to do so had not yet been collected.
A map of the castle from Resident Evil 4 is displayed on monitors after the final credits. Those events don't happen for another year, and no Resident Evil character would know anything about the Resident Evil 4 region at this point in the time-line anyway.