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 ...