Are you sure it was the xc3000 that was documented and not the xc6200 series (e.g. xc6264)? I remember the xc3000 being documented the usual amount for their parts (pinout, architectural description, call for info about licensing the software you need to have to use the thing), but the xc6200 datasheet definitely included details about the bits and is still floating around: https://duckduckgo.com/?q=xc6200.pdf