Secondary sources are always a problem for the researcher! I'm one of the editors on NPOR - and it's amazing what some published information says - I came across an example just last week where the wrong organ builder was credited with a rebuild! (Actually, that's not too uncommon - it's usually Hill that's quoted, simply because the Hill firms estimate books have survived, and it looks like they submitted prices for vast numbers of organs that subsequently went to other builders. Researchers see "Hill2 and make 2+2=5. Even leaflets, etc circulated by organ builders can contain errors - especially when a stop list is circulated before the organ is finished - stops sometimes get moved around, or substitutes made during the building phase - and as for organ magazines! A recent edition of one (that will remain nameless - regular readers may well recognize it!) managed to print - on the same page - pictures of an organ's stop jambs and a stop list. They were not the same!
I had a similar problem in my studies. I decided to write a history of the church that we were Ministers of at the time - BIG mistake. There was very little information available - and after writing a lengthy essay, with the idea of eventually publishing it - I ran it past a friend, who I then discovered was a historian, who gave me the "good" news that one of my main sources - the only published history of the village - was grossly inaccurate! (I still got good marks for the essay - but the publication never happened!)