Do I have a valid argument to ask them to stop parking in the spot next to me since there are spots they don't park in for that spot is someone else’

I live in a condo complex with townhouses spread over multiple streets. There is no assigned parking per the condo's rules. However there is an unwritten rule of people 'having' their own spots. I live in one building where 30 feet away are 3 spots, in the first one a condo board member parks, the second one my husband parks in and for the last 7 years someone from an adjacent building with close proximity to the space has been parking in. Now for 7 years this is how it has been. Recently the 3rd spot came open when that family moved so I started parking my new car there. Someone who is retired from the other side of the adjacent building has started parking in that spot whenever I leave for work or go out. Now they have parking available near their condo and for 7 years have been parking somewhere else. Just recently this car from the other side has started to take over the spot that I would like to park in and have been parking in since December. The excuse that they will likely use is: "it is the rule that you can park where-ever you want since the rules state no assigned parking." To test that theory, I moved my husband's car over to that spot and his middle space remained open. They did not park there but waited until the 3rd spot opened up and parked there. Also tested the spots in front of their building and they can park there and the assumption is they don't because those spots "are someone else’s". I know the board members will state that there is no assigned parking but my argument would be that this person does believe in this or else they would be parking in front of their own building instead. Ergo because they believe that then they need to respect that because this spot is next to mine.