Learn English – the difference between “I was there” and “I have been there”

Keep in mind that a present perfect casts its predication in the present tense. It does not narrate past events, it mentions past events which give rise to a present state.

That is why formal English does not permit a present perfect to be used with a temporal adjunct which does not include the present moment, the Speech Time at which the sentence is uttered. (You will occasionally find this rule violated in improvised, conversational discourse; but even there it is comparatively rare.) Thus, this is acceptable:

^okI have often visited London.

But this is not:

^∗ I have often visited London in the 1990s.

Today, in the 20th century is a timeframe which excludes the present. Consequently:

• Sentence 1) is acceptable if it appears in a text written in the present century, but would be of questionable acceptability if written fifteen years ago.

• Sentence 2) is acceptable if it appeared in a text written during the 20th century, but it would not be acceptable if written today.

There is a great deal more about this at What is the perfect, and how should I use it?, especially §§ 3.1 Grammatical meaning, 3.2 Pragmatic meaning and 4. When and how should I use the perfect?.

^∗ marks a usage as unacceptable

Let's say that a colleague mistakenly believes that Joe is a new hire. We might say:

Joe has always worked here.

to mean nothing more than the fact that Joe is not a new employee. He has been here for some while.

If we want to say that Joe never slacked off when he was working at Acme Widgets, but always took his job seriously and gave it his best effort:

Joe was always working when he was at Acme Widgets.