I don't think that this number is all crew, nor all disappearances. I think the actual number is from the Cruise Junkie website. It is a total number of all overboards passenger or crew from Cruise ships and also ferries. Plus the 171 number quoted in the article does not account for the fact that some went overboard (some by their own volition and some not) and were then rescued.
Also I think that the reports are all a compilation of media reports, not a peer-reviewed source. So in actuality the number may be incorrect altogether.