Delete old versions of backup without running a new backup

All right, that works great.

Now, is there also a way to delete, let’s say, nine versions out of ten in one go?

I tried this:

–version=11-19
–version=21-29

As a result, versions 21 to 29 were deleted. The first line was ignored.

I thought of trying this (but didn’t dare):

–version=11-19;21-29

Would this work?