Because I live in Chicago, have a very large chicago collection, know most of the Chicago records I don't have (although there always are new ones I'm finding about, mostly from the 80s though), have looked through other large chicago collections of other collectors, have talked to members of the Lintons, and actively look for and discover records I don't know daily.
It could be a typo that made its way into his system. Does it have the same catalog number? If so, definitely a typo. if not, maybe worth investigating. There is another very rare record on essica by the sharpees that nobody knows about so there is a possible connection. There's always stuff popping up that nobody knew existed before, so I can't say 100%, but I can say 99%