That's weird.
Your vendor, Bill, is not the actual manufacturer of all the postmarking devices.
But he should fix somehow the problem.
I have no problem with the self-inking dated stampers from him.
More recently, I ordered from him empty-of-date postmarking devices, and I bought from him a separate date-stamper.
Why? Because when the date-stamper reaches the last useable year, then I can re-order just the "next years date-stamper", not the rest of the postmarking device.
In your case, you could also use a separate date-stamper (month, day, year) AFTER you apply the impression of the "empty" postmarking device.
My first MPP, all-leveled:

The date-stamp I added AFTER the rest of the postmark:

It's a manual operation, and sometimes you might press too hard to get a visible date-stamp. Here I tried 3 times:
