Are entries ever removed from the Merck Index? I was re-sorting books the other day, and thought about how many years it has been since I bought my Merck Index. I'm sure there are new entries in the more recent additions, but I do not have such a need to stay that up-to-date.

At first thought, it seemed to me that a book of this nature only adds entries, and does not remove any entries. But is this the case? Are compounds de-listed because they are bad science? Other reasons?

Iit would be great to know other details about the editorial process, as well, if relevant.
Without several print editions side-by-side, I restrain my answer to the electronic version. This public link or here regarding the online version based on the 14th edition may be read like it may be the case.  To quote:

 "The 14th Edition also contains "retired" records from earlier editions of The Merck Index which still contain valuable information but are no longer being updated with new information."

Of course, beside RSC you may contact them (Merck in Rahway, NJ), too.