It would help to know the relationships that link your tables. You indicate that you have portals but not the relationships and any possible portal filters used to set them up.
At a guess, it sounds like you have a many to many relationship between clients and artwork facilitated by join table linking the two. But while that would match the description you post, other combinations of tables and relationships could as well. If there is a join table between Artwork and Client a field in that table could record the appraisal date and another field or group of fields could record the new location of that artwork.