The tagging is OK. Things seem to be working properly.
That tagging rule
You're referencing a rule we have for the D&D tags where we don't use dungeons-and-dragons if we're only asking about a specific edition, but that rule is only for the D&D tags.
The default is just "tag with whatever makes sense at the time". Questions for fate, gurps, rolemaster and others frequently get a series tag as well as an edition tag because it makes sense at the time. There's no standardisation there and I'm not aware of any pressing need to establish any.
Apparently that rule for D&D tagging was created to resolve some problems:
The “do it whatever way suits us at the time” is the default, yeah. For those who weren't here for it, the only reason D&D gets special treatment is that its tags started to cause problems and needed stronger guidance. – SevenSidedDie♦ Apr 5 at 17:38
I'm one of those people who wasn't there for it so I don't know about the specifics. By the time I was properly active here the D&D tagging protocols had already been pretty much sorted out.
The Rolemaster tags
The Rolemaster system involves a lot of editions and offshoot material (first edition was 1980, fourth edition was 1999). Its fans use "RM2" colloquially to refer to first and second edition material, which the rolemaster-rm2 tag wiki excerpt clarifies. That works for the Rolemaster community, so it's good enough for us. That tag was originally just rm2 but worked its way into rolemaster-rm2 instead to clarify it's a Rolemaster tag.
The rolemaster tag refers to the whole series. There's also rolemaster-fantasy-roleplaying and rolemaster-standard-system.
If the Rolemaster players here feel like it needs to be sorted out a bit further or they need some standardisation, that's up to them and they're welcome to discuss it here on Meta to figure it out. But the way it currently is working is OK per site protocols (specifically the default "tag it however" protocol 🙂), and appears to work for Rolemaster players well enough, so it doesn't need any specific intervention right now.