I'm not quite decided on {ta'e}, although it seems that the habitually meaning is worth preserving, unless there's some overwhelming evidence from usage indicating otherwise.
In my opinion, trying to treat all TAhE in the same way when used as sumtcita isn't worthwhile. In particular, I think that {di'i} as a sumtcita is far more useful for tagging the frequency (the interval between occurrences) instead of the general interval over which the whole thing lasts. If you want "regularly for three years", you can get that with {di'i ca lo nanca be li ci}, but if you want "regularly, once every three years", then that should be {di'i lo nanca be li ci}. It's an argument from pragmatism over regularity, but I think it's a meaningful one.