It's not uncommon. It's easier to collect than it is to classify. Eg, here's a news report from 1988 about how "[a] 70-foot dinosaur known as Happy stood prominently on display at the Cleveland Museum of Natural History for nearly 25 years before researchers discovered it was a new species." http://articles.latimes.com/1988-09-25/local/me-3747_1_natur...
It points out that "Museum storerooms have become rich hunting grounds for new species because a lack of money and staff has delayed the identification of bones excavated up to 60 years ago" and that "75% of the museum's collection has not been examined closely."
It points out that "Museum storerooms have become rich hunting grounds for new species because a lack of money and staff has delayed the identification of bones excavated up to 60 years ago" and that "75% of the museum's collection has not been examined closely."
Nor is it a recent issue. The HMS Challenger expedition of 1872–76, which was the first real oceanographic expedition, took another 19 years to publish everything. (See http://en.wikipedia.org/wiki/Challenger_expedition#Findings_... ).