Bill Gates did not write it by himself, Paul Allen and Monte Davidoff also worked on it. And they did not have a finished product after 8 weeks -- only a demo. The first commercial release was "version 2", half a year later.

How would Bill Gates copy source code from a 36-bit minicomputer with 32 kilowords (no byte addressing) of memory and a time-sharing operating system to a 8 bit microprocessor with a completely different instruction set and 4 kilobytes of memory and no operating system, just bare metal? Even if he and Allen had had the source code for BASIC-10, which you haven't provided evidence of, it would be closer to a reimplementation than a port.

And DEC was in Massachusetts, Bill Gates went to high school in Washington. That would be one hell of a road trip to dig into DEC's trash.

None of us write programs from first principles, it's all based on code we've read before. If I was going to write a BASIC interpreter I'd read up on the basics of interpreters, literature which would include sample code, and look at other interpreters' code.

No matter where you think the code came from, the impact of Microsoft BASIC was huge, and they were first to the market.

BASIC was " BASIC, developed at Dartmouth College, was initially designed for and ran on a GE-225 mainframe computer paired with a Datanet-30 processor, which handled communications with Teletype terminals. " I got into the game on HP BASIC, also with teletype ASR-33s, I was only 9.