Yes, but AMD was only able to push AMD64 as an Itanium alternative for servers because they were having something of a renaissance with Opteron (2003 launch). In 2000/2001, AMD was absolutely not seen as something any serious server maker would choose over Intel.
You're right, there were ebbs and flows in their influence...but they were consistent in those trends. Releasing an extension during their strong period was almost certain to be picked up, especially if Intel wasn't offering an alternative (which Itanium wasn't considered as it was server only).
