Microsoft’s original source code

Microsoft got its start by Bill Gates doing some dumpster diving. Back then software wasn't seen as valuable thing, only hardware was. Source code wasn't something to be protected, so printouts of code would be thrown in trash. And that's where Bill Gates found the source code for Basic interpreter, which he ported and it became the first Microsoft product.

https://americanhistory.si.edu/comphist/gates.htm

https://paulallen.com/Futurist/Microsoft.aspx

> "...so printouts of code would be thrown in trash. And that's where Bill Gates found the source code for Basic interpreter, which he ported and it became the first Microsoft product"

Both sources you link to say Allen and Gates pulled listings of the PDP-10 operating system out (probably DEC's TOPS-10?) of the trash. BASIC is not an operating system. So your claim is debunked by your own sources.

"...digging out the operating system listings from the trash and studying those. Really not just banging away to find bugs like monkeys[laughs], but actually studying the code to see what was wrong."

https://americanhistory.si.edu/comphist/gates.htm

"...He and Bill would go “dumpster diving” in C-Cubed’s garbage to find discarded printouts with source code for the machine’s operating system..."

https://paulallen.com/Futurist/Microsoft.aspx

That article is a bit confusing because it's using the term "BASIC" to refer to both the language and Microsoft's implementation. But what it's trying to say is that Microsoft's BASIC implementation was licensed by many computer companies (including Commodore and Atari) and that those companies changed and extended it in incompatible ways.