Pure - I don't know about the process in herptiles and plecos, but know a considerable bit about it in plants and fungi. Quite a lot more molecular (DNA) work has been done in fungi than in most animals, because there are considerably fewer morphological features on which to base descriptions, but a big part of the process (and delay) is still in seeing whether the species in question has even been described before. A lot of nomenclatural confusion results when proper literature searches haven't been done, and the same organism gets named and described several times. One specimen may have been found, described and validly published - in 1872, in Kamchatka, by somebody publishing in a specialist Russian language journal of limited distribution. First, you have to even be aware to look at this journal, track down the article and, if necessary, obtain translation. Suppose you find your plant/fungus/pleco/lizard in Java. It matches the description of the 1872 Kamchatka specimen. Is it the same? - Historically, there's been a lot of trouble occasioned by European taxonomists calling things they found on other continents by European names because they looked similar, but in some cases species really do have worldwide distribution. Then there are some potential difficulties with DNA - at the time of description, species are supposed to have an associated "type specimen" deposited and kept for perpetuity where any researcher can examine it and make comparisons. For plants and fungi, these are usually dried specimens, and one can sometimes still obtain sequencable (albeit degraded) DNA from them; a pleco would likely be pickled in formaldehyde; lizards would be stored in a variety of manners (pickled; taxidermy specimens), none very friendly to DNA.
That's almost certainly more than anybody wanted to know, but I'm a taxonomy and nomenclature nerd. ("Nomenclaturists are a bunch of frusterated, lawyer-type people who accidentally ended up in science." Jim Groth, a onetime professor of mine.)