Shamus had generic plates for about a week or 2 during his run last year. Considering his cash in was a last minute thing this might give us some idea.
They must have either known ahead of time or they have key guys plates made backstage.
I like to think there is a locked room at the HQ where they keep custom belt plates for every superstar on the roster.
Somewhere, even Kalisto has a custom belt plate set.