If I had handwritten this, there would be at least one (likely lots more) errors in writing crossed out mingled in with the text. That there isn't makes me wonder why such a lengthy sample contains seemingly zero handwriting errors. Is that plausible?

EDIT: After seeing the comments, I am realizing how little I ever rewrote my own writings, an admitted weakness of mine. It was the blindspot behind which I made my reply!

You can handwrite more than just your first draft. It was common before the proliferation of computers to handwrite early drafts in pencil, and then handwrite the final manuscript with ink.

You can write a draft first and then transcribe it once it's done without any mistakes. That's how I had to write essays when I was at school.

In grammar school in the 90s, I used to write in pencil, then retrace in pen when done, erasing the underlying pencil after the ink dried. I'd proofread the pencil version, find missing words, and you could rewrite to balance out space

I think that was pretty common amongst "keeners" doing writing assignments.

Yes, your bias is showing. Before Gutenberg, "scribe" was a profession, and perfect fidelity was expected.

We also don't know how many sheets went in the bin.