Species1951,
You are correct, here is what Mike at CZ-USA emailed to me.
"The main difference between the compact 75 magazine and the 100, 9mm is the
magazine latch cuts are different. They are located close enough together
that a 100 mag can be converted to a compact mag, but not the other way around.
I have been trying to get hi-cap mag bodies for both of these pistols and have
only now recived a good supply of compact, hi-cap mag bodies. I will keep trying on
the 100 hi-cap bodies, and when they do come in, will only require a tube switch
with the 10 rounder".
However, Mike says that the compact 13 rd tubes are available and are $27.44, and will only require the steel compact mag base at $4.91, to convert the ten rounders.
To order with a visa/mastercard, call Mike, CZ-USA, at 1-800-955-4486.
I'll repost the availability of the compact 13 rnd tubes on the Compact Forum.
Dave