The "useVMR" registry name is a misnomer. It initially was meant to be just that (use VMR or Not). It later evolved to really mean "which video renderer". Currently (since the selection became available to users) 0 means LVR, 1 means VMR9, 2 VMR7, 3 EVR. So if you set the value to 0, it is equivalent to selecting Legacy Video Renderer in latest builds only. However, before the selection was made available to users, for a long time the value of 0 meant "not making any specific selection". Depending on systems, this could mean either LVR or VMR7. So you could be using VMR7 when you thought you were using LVR (when you set the registry value to 0 manually). Windows XP uses VMR7 as default video renderer unless the hardware does not support it.
Confused? My apologies. In summary, maybe VMR7 was what you had been using when you thought you were using LVR.