That and there were never official grammars published for any version of any basic from Microsoft afaik
I had to write a VBScript parser some 25 years ago (to syntax-check ASP files before they would crash live) and to get it to parse valid syntax correctly, I ended up with a messy patchwork of logic which was also letting through some really pathological edge cases. While trying to fix it, to my utter delight, I found that Microsoft’s parsers also allowed the exact same cases which looked nothing like valid code otherwise. I don’t recall specific examples anymore, but they were far from obvious without looking at the parser code, and I made and won bets with other programmers on whether those snippets would throw syntax errors or not.
Probably right, since Microsoft's BASIC interpreter is probably derived from the one that Bill Gates wrote as a teenage slacker. He wrote it, tried to sell it at the homebrew computer club, and then threw a hissy fit when people kept copying his paper tapes for their friends. Thus, Microsoft was born. (He got lucky later when Microsoft were chosen by IBM to develop a DOS, then bought a working DOS from somebody else. The rest as they say is history)
They had compilers for many programming languages, but before buying the operating system that they have rebranded proudly as MS-DOS and which they have resold to IBM at an overprice, they had nothing to do with operating systems.
So the deal had nothing to do with their previous technical competence, but they happened to know the right information about who is selling and who is buying, which allowed them to gain the most as the middlemen.