A ‘contingent thing’ is something whose existence is not necessary: its non-existence is possible. For example, something that can begin to exist would be a contingent thing since its non-existence would be possible.

A maximal collection of contingent things is a collection of contingent things that cannot be contained in a bigger collection of contingent things. For example, a maximally dense object O whose nature is to fill up all of space, plus any and all possible non-spatial contingent things compatible with O, would form a maximal collection of contingent things.

Is it possible (logically possible) for a maximal collection of contingent things to begin to exist?

No I don’t know Yes