Nick Hacko, I have the answer for you>>>

[Jocke]

I just talk with a Rolex trained watchmaker and he
told me the "dummy jewel" is to support the date wheel
when it change date. I suppose it will slide a
little when it change date.

Does that sounds ok in your ears?

I hope that because the guy I know is one of the best when
it comes to Rolex movements.

Jocke