Well a lot of these names are quietly given to these things, but also doesn't appear as part of the ongoing marketing. When I searched for the name of the 600's, I only ever found them called "avantgarde" in old magazine articles from when they were initially released, but never saw that moniker used thereafter. They might even be names that were included in the product manuals, but then taken out after the initial manufacturing run.
Here's the video for you
I've owned the Sennheiser HD700 phones since 2016 and have never seen that video before today. Never even heard that moniker used with them.
Anyway, I'm still using my HD700. Will be modifying the Black Dragon cable I got for them with a 4-Pin XLR balanced connect, so I can use them with my Denafrips headphone amp in balanced mode.