The reason those SR9s from 1998 were not stamped is...they weren't SR9 Ts and TCs. HK was trying to get permission from ATF to bring in SR9s again, but they got shot down; no new SR9s allowed; no new SR9s imported. They even had a new stock configuration, but they were nothing more than a photo mock-up of what they wanted to import.Do not open this can of worms........ I have a 1998 HK Catalog that has both the T & TC not stamped. No one knows for sure who, where, or when these riffles were stamped, just a lot of educated opinions from collectors.
As long as you are happy with your HK, that is all that matters IMHO