The brain doesn't typically rotate inside the body - a person referred to as left handed today was the same as someone left handed 100 years ago... Got it? -- some of us are even old enough to know people alive in the 1920s and prior, but there are plenty of books to confirm this... the prevalence of right and left handedness didn't swap sometime recently.

The left brain is the side of the brain that is on the left side of the body. There was no reason to ever make it more complicated than that.

100 years ago is not that long ago - so the snark is more about the "how can we possibly know?!?!" tone - you can look it up - I think 1800s editions of Gray's anatomy are scanned online. Wikipedia still uses the fucking things from the 1910s because they're out of copyright - https://en.wikipedia.org/wiki/Human_brain#/media/File:Gray65...