Child custody with unsigned agreement

We have an unsigned agreement in which the children are with me every other weekend and an optional wednesday overnight. For the first month they were with me every night, then started the schedule 4 months ago.

In the event that he never signs the agreement and wanted to get custody from me, would it matter at all that we had already started an every other weekend pattern that was working for the kids? Seems like a judge would require him to prove that the current arrangement was determental to the kids in order to get custody.

Just trying to cover my bases since he refuses to sign anything.

The schedule can be used as evidence as to what the children are accustomed to, and argued that it is (or is not in their best interests) but will not be controlling in a court of law.