It is interesting you bring this up, I was thinking about this the other day. I think this is a good point.
Perhaps it would make more sense to merge them? I have been adding the Orange3 tag to relevant questions recently thereby increasing it use - however I am not sure any question asked recently refer specifically to any earlier versions of the software. For reference Stack Overflow only has one tag
Orange and does not have a separate tag for
An analogue of this would be having a
python tag and a
python2 tag. The latter is not likely to garner much use as older versions become superannuated.
More explicitly - I do not think having a separate tag for versions makes the most sense as likely almost all questions asked at this time will be included in this subset as you mentioned.