That's true PD it does help to have a good library, mine is now growing lol.
However when the names are so confusing and get changed because some scientist decides it doesn't belong in that species anymore, it's enuf to drive ya nuts.
Take Stenocactus - which is it Stenocactus or Echinofossulocactus? I would not like to try doing a thesus on cacti, by the time you finished the names would all be wrong!!!! lmao!!!
Also a lot of the pictures you look at seem to be similar, so what do you look for? Number of spines, ribs, columnar, globose? Or does it come down to wait for it to flower and hopefully decide then what cactus you have?