Have you tried an extended timeline mod?Is it possible to browse an ironman campaign at 3 January 1821 or I can only view the timeline via end game screen and other in-game tabs are inaccessible?
Obviously, back up your save file first.
If the mod works the way I think it does, you should be able to open the save and browse around to your heart's content. However, I haven't actually tried this (I've made it to 1821 precisely once), so I don't know if this'll actually work. But it's not too big a time investment, so it's probably worth a shot.