This is not the earliest microSHIFT catalogue that I have on this site, but it is the first one that shows rear derailleurs.
It features a range of six, closely related, mountain bike derailleurs. The range is composed of three levels of quality with two pulley cage lengths at each quality level. The basic design is very similar to the microSHIFT M55 in this collection.
Many thanks to William Chen for these scans.