Here's a fascinating (and maybe even slightly on-topic!
"In universe", the obs lounge model artwork we're all discussing vanishes completely without explanation halfway through the series' run, never to return again (chronologically speaking, that is... it *does* pop up again in the 'past' segments of All Good Things
Do any of us have any wild theories why this might be?
Just a simple remodeling of the briefing room?
Maybe Picard just decided he didn't like how the wall looked and thus ordered it replaced.
As for Saavik: Like all recasting, it doesn't need to be explained. Characters change actors all the time. Saavik no more needs an explanation than, say, Admiral Paris.