Flashback got a lot wrong in regards to TUC. In Flashback, Sulu takes the Excelsior into Klingon space to rescue Kirk and Bones a few days after the Praxis explosion. But in TUC, few months go by after the explosion before Gorkon and his staff arrive on the Enterprise for dinner. Honestly, Tuvok has a faulty memory is the best excuse for everything. Valtane, timing of the Praxis incident.
But the part that really bothers me is when Janeway looks up everything in Starfleet records, which includes the Excelsior's sensor logs on the nebula and a log entry from Sulu saying the ship is undergoing minor repairs. Why is this in the starship's database? Wouldn't it be more convenient for it to be in space Wikipedia, or Memory Alpha which starship crews can access via space internet? Sure, that would mean the Voyager crew wouldn't have access to this, but really does Starfleet actually load up each starship's database with every sensor readings the ship made and every mundane captain's log entry? Besides, how the hell does someone read a log entry from Sulu saying his ship is undergoing minor repairs and decide "starships 80 years in the future are going to need to know that."