Yes it did. "Sit" is the classic format, and "Sitx" is the modern format. From Wikipedia: "[Stuffit X] was designed to be extendable, support more compression

Yes it did. "Sit" is the classic format, and "Sitx" is the modern format. From Wikipedia: "[Stuffit X] was designed to be extendable, support more compression methods, support long file names, and support Unix and Windows file attributes. StuffIt X improves over the original StuffIt format and its descendants by adding multiple compression algorithms such as PPM, and BWT to LZW-type compression. It also added a "block mode" option, error correcting "redundancy" options to protect against data loss, and several encryption options. In January 2005, JPEG compression was added as a StuffIt X compression option" Unlike the original Stuffit format, Stuffit X never saw any significant use, since Mac OS X had switched to Zip as its default archive format.