The whole point about this site is that folk singers etc. try and get to the bottom of where a song comes from. It is your responsibility before you post to try and ascertain where a song comes from. Different if a song is trad. or you are just asking about the origins or a full set. Don't post lyrics at all to be permanently stored unless you are sure. You can sometimes help set the record straight... like as you say McLean's...Glencoe.   It's the thing of common sense. Unfortunately many singers and recording artists or their record companies are totally ignorant, or chance their arm making false trad. claims. on modern works - or just make errors. Frequently there will be printing errors on old record covers. It's different for me as
I can look up the MCPS/PRS copyright society database and do a check to see which is likely to be the most accurate registration. The collective mind of Mudcatters is also often a good research tool. If you are unsure, ask others before you wrongly attribute lyrics to be permanently stored.