A general question; might be of interest/relevance to the OP specifically, but anyway might have relevance for the general proposition of multi-boot Linux distros with common
How do you manage third-party programs with critical reliance on their accumulated user-data? Two suitable examples might be Firefox & Thunderbird, which you intend to use regardless of if today you booted into Linux1, Linux2, Linux3 etc. I'm also making the rash assumption here that irrespective of your boot choice today, you still intend being You, not a different user, ergo you want all your Bookmarks, Tab Sessions, UI layout, emails, calendar events yada yada in FF & TB no matter which boot is currently active.
However, Linux1 might use a different version of FF &/or TB to Linux2, or Linux3, which might have adverse implications for your common
So what do you do, how do you manage such scenarios, how do you have your cake & eat it?