Determining lost value for title claim

[Braden Hobbs]

Hello. I have a 4-plex that I had planned on updating and re-spraying the lines for the large parking lot in front of it. While preparing for this, my property manager was given an easement by a neighboring unit's owner that was created that makes the lot shared use for the 2 neighboring buildings (also shared maintenance and cost for updates etc.). This easement was missed by title so we have grounds for a claim.

My question is how would you go about determining the loss in value for owning the parking lot outright, versus it just being a common space?