I still reckon the decision about whether to take action depends on whether it is a problem now or likely to become one in the future. Where I am, we have several residents with more vehicles than they have allocated spaces but this has not caused any practical problem for residents or visitors. There is sufficient unallocated parking and street parking and some private arrangements between residents for unused allocated spaces. It has been like this for several decades so it seems unlikely to become a problem any time soon.
A middle course if it is not an immediate problem would be to write to the person parking on common property pointing out that they have no right to park where they are and no recourse if others park there and the OC might need to enforce its parking rules if demand for parking were to get tighter.
We have had some other serious parking issues but this was not one of them.