I'd say you probably could say «vIta'be'pu'.» and be understood, but «vIta'pu'be'.» is more categorical: Not only has there been an instance of me not doing it, but also there have been no instances of me doing it (in the scope of time being considered).

I don't think there's any difference in meaning between vIta'be'pu' and vIta'pu'be' as far as anything we've ever seen. The difference between completing not-doing and not completing doing seems too hair-splitting for Klingons... or even English, since I have to resort to made-up terms like not-doing to describe it.

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SuStel
http://trimboli.name