Shared CCACHE_DIR, different ccache releases?

How can I know if it's OK to use different versions of the ccache program with the same CCACHE_DIR location?
We would like to use ccache version 3.1.8 and 3.1.9 together (depending on the version of the OS-provided tool chain we are using).
I just want to be sure that the structure of the cache has not changed so much between these releases that the CCACHE_DIR can't be shared.

Also, what is the convention regarding the version number? For instance, if only the last number changes as is my case, should CCACHE_DIR be generally compatible?

Thank you,

--Edwin

Edwin Jacques
Development Enablement
Core Technology Division
EMC2 Corporation