Hmmm. I think it has to do more with the tense that you use. I'm not a
student of English, but rather a native speaker, so I can't always explain the
rules of grammar to you…but in my experience:
I have been TO the USA <in my lifetime>. No timeframe is
necessary. This is a completed event.
I have been IN the USA. Usually this sentence will continue with
some kind of timeframe – „…since last Tuesday / for 20 years / since
I was born.“ Otherwise it sounds a bit Czenglishy.
I was IN the USA. This also implies a completed past event.
Timeframe should be specified if not stated in the question that this
answers – last summer / 20 years ago / on Tuesday. Where were you last
summer? I was in the USA." or "I was in the USA last summer.
I went TO the USA. Again, timeframe should be stated if not in the
immediate context – „Where did you go last summer? I went
to the USA.“ OR „I went to the USA last summer.“
I went IN the USA. – This is just plain wrong!
Does that help or just make it more confusing?