Amazingly, not a topic bashing the program!
I do have a question... what is the oldest version of the program we can get? Did it start on Windows 3.1 and work it's way up?
I don't remember there being an official mech editor for the PC in the 3.x days. I remember using one that you plugged the sheet details into a formatted text file and it would generate you a record sheet based on it, and that was pretty good for the time, but of course you had to still design the mechs yourself with a spreadsheet or pen and paper.
The big Record Sheet books (3026&3026, 3050, 3055&3058) had a note in the front about an official editor for Mac, but not PC.
According to the HMP website, Rick Raisley developed the first version of the software for DOS in 1993, started discussing the idea of licensing it with FASA in 1994 but they wanted a windows native version, which he initially submitted to them in 1995. The first licensed version of Heavy Metal came out in 1998.