Well analysis of measurement data can be done elsewhere, even if taken from one alien at one base. If you went on with your thought of how many can work on one alien, it would be even more ridiculous that 250 people are researching one alien, even if they are all working on the same base. So for the sake of game play that could be overlooked. (But would be an interesting mechanics, that there is a limit of researchers per item, depending on the type of item.) At least when thinking of the research items that don't require any particular precursor (e. g. laser weapons), then things aren't that obvious any more. So I believe the question is quite legitimate. The fact, that this detail it not really mentioned anywhere is strange, but can be rectified. ;-)