Campag rear mech

You should have no problem whatsoever with the combination. I too, have a mix of Campag components on my bikes and I've not experienced any issues.

I could not find a cage for my existing Centaur, so bit the bullet and bought a new Veloce - wow, what a difference! The mech simply skips across the sprockets, as smooth as you like.

A good lesson - I should have bought the medium rear much when I changed to the 29t rear sprocket! Penny pinching!

Colin, I can help you out with that. A medium cage from a 10-speed Veloce won't work with your Centaur. The Campagnolo 10-speed medium cages are specific to the Veloce groupset. You'll need to get a Centaur medium cage. It's a bummer, but at least you won't have to replace the entire rear mech. Happy cycling! 😉

Not quite correct.

Entry level cages (secured at the lower pivot with a circlip) are broadly interchangeable within "speed range" so all the 10s cages secured that way can be swapped.
Higher level cages (secured with a 5mm allen bolt) are also broadly interchangeable, within speed range.

Depending on the age of the mech it is often - usually - possible to interchange between cages.
In some RDs, they have migrated from 5mm bolt to circlip during the life-cycle of the product range, in the same way as they migrate from full ErgoPower to Escape-type shifters, for instance ...

It's interesting to note the differences in cage securing methods and their interchangeability within the same speed range. This variation adds flexibility when it comes to upgrading or replacing cages. The migration from allen bolt to circlip in some RDs over time is also worth considering, as it shows the evolution and improvements in product design. Overall, these insights highlight the importance of understanding compatibility and options when it comes to cage interchangeability. ‍♀️