If someone provides too many details on something, basically making it more difficult to extract the actual information asked for, what is a good expression to describe this? Is superfluous adequate or too harsh? Would it make a difference whether the too-much-information was on purpose or inadvertently?
If someone 'provides too many details on something actually making it difficult to get the needed information out' a word that could be used is 'verbose'. This is an adjective which means too wordy or using too many words as in a write-up or a speaker addressing an audience.
Please see my comments below first.
My second offering: circumlocution (n.) - the use of unnecessary wordy and indirect language. The adjective is circumlocutory. An antonym of a circumlocutory expression would be a forthright expression.
information overload (n.) the situation when someone has so much information that they are unable to deal with it
Another (CDO) says:
information overload (n.) a situation in which you receive too much information at one time and cannot think about it in a clear way
Thus, the danger of “information overload” is real; if any user were to receive all, or even a significant fraction, of the total amount of data contained in the system, he would be hopelessly swamped. (from Strategic Appraisal: The Changing Role of Information in Warfare, Rand Corporation, 1999)
When you supersaturate somebody with information beyond their immediate requirement it is translated into an information overload. You end up making a mess of the whole matter because the recipient probably will even lose whatever vague initial understanding of the subject they had.
This is almost a normal occurrence when a postgraduate science student is asked to teach science to an eighth or a ninth grader. It is indeed an innocent curse because the elder is after all trying to help out the kid but unfortunately ends up messing it up.
Of the Wiktionary synonyms for superfluous (excessive, extraneous, extra, pleonastic, supernumerary, surplus, unnecessary, extravagant), extraneous actually sounds best, since it means both "not essential" and "not belonging to". But please note I'm no native speaker, so the choice may be sub-optimal.
While I think @TobiasKienzler has some good alternative suggestions, this suggestion of 'esoteric' may or may not fit, depending on what kind of details they are.
From the additional context found in comments, it suggests that 'esoteric' isn't quite on target because the extra information is not necessarily difficult to understand or appreciate in its own right. I would be more inclined to go with a word used in comments to describe it, 'superseded' as it more aptly describes why the information is extra.
1 a : designed for or understood by the specially initiated alone
1 b : requiring or exhibiting knowledge that is restricted to a small group ; broadly : difficult to understand
2 a : limited to a small circle
2 b : private, confidential
3 : of special, rare, or unusual interest