Having been around when these Macs were new, here are a few things I can tell you for certain:
--Macs in the System 6 era used Macintosh HD as their internal hard drive name. The SE/30 on eBay right now provides proof of that, although I can also say with 100% certainty all Macs with internal hard drives had this as their disk name. This has continued ever since with one exception.
--Performas had Hard Disk as the name. I think part of it was to make it easier for new users, part of it was to separate it from regular Macs.
--Don't forget there are regional differences. Macintosh HD was the default in the United States, but it may have been different in other countries, as we've seen pointed out here.