From what I have seen over the years, All RouterOS packages upgrade together. (All packages on one router MUST be the same version).
Routers of a different version will still be able to communicate, but it has been my experiance that if you create tunnels, it is best that the routers at both ends be the same version. You can have issues of the tunnel being eratic or not comming up at all if the routers at both ends arrent the same RouterOS version.
In general I try to keep all of my routers updated together.
Things that make you go "Hmmmmmmmm"...