So the MMU only had six untethered EVA's?
It was my unsuccessful attempt to find out how many untethered EVA's were performed with the MMU and the newer SAFER packs to date that led to the 10 year gap. If all were in 1984 you answered part of my question unless the MMU was used along with Safer in later EVA's.
I thought that some work on the Hubble repair missions were untethered using the Safer unit but couldn't confirm it either.