Century 21

Just out of curiosity, is anyone familiar with Century 21 shorthand?  The other day, I saw a copy of the instruction manual for this system and was very surprised to see that it appears to be, more or less, an only slightly modified version of GS (in one of its post-Anni versions).  Yet, the manual makes no reference to Gregg in either the copyright info or the preface.  Was Century 21, formally, a GS system (it's also not mentioned on the Angelfishy site, so I'm assuming not).  Was it in total violation of GS copyright?

(by A for everyone)