The present perfect is used when the speaker has in mind or wishes to signal that the finished action or state occurred in some timeframe that has no terminal time boundary in relation to a main time period (now/time of speaking/in this class). The earlier/previous studying occurred in some timeframe (the semester/term of the course) which has not yet terminated, at least in some sense—or it’s not considered or not seen as important to specify.
We have studied it [e.g., earlier in the course/before this class in the course, with the course continuing at the time of speaking].
The past simple is used when the speaker has in mind or wishes to communicate that a finished event or state occurred in some timeframe which finished in the past—or it’s not considered or not seen as important to specify.
We studied it [in past classes, which have ended].
The “past simple-exact time” idea is only a sort of rule of thumb: a specific/precise time is sometimes specified, but this is not a reliable rule. It quickly breaks down under scrutiny: I was born in France. (No time or specific/exact time was specified, yet we must stretch to find narrow contexts in which the present perfect would be used here.)
The “connection to the present” notion likewise often makes little or no sense. *I was born in France” certainly has a connection to the present. I’m alive now. Any past thing we mention now has a connection ton the present: We’re mentioning it in the present!
American speakers of English more often interchange the two tenses, while British speakers of English face more strict pressures to make a choice and convey it via aspect.
Earlier and before have the same meaning in this context.