On the contrary, Maguire likely would NOT have used a spellchecker - this was mid-90s, when checkers were not automatically running in background and had to be explicitly (and painstakingly) invoked, Jerry is writing in a fevered state in the middle of the night, and he's a high-powered sports agent with a personal secretary. Low editing quality would be expected by such a guy in such a state, it's already good that he does not WRITE IN ALL CAPS AND WHAT IS PUNCTUATION RHONDA.
But yeah, the typo are likely unintentional by Crowe - in the end this is just a prop, and as I mentioned automated spellcheckers were annoying back then.
It's also likely he was using something like Final Draft to write the script (which really focuses on formatting first). In all honesty, I wonder if it even had a Spell Check feature back in 1996, assuming he was even using the latest version then.
Heck, Microsoft Word didn't have automatic spell checking (always working in the background) until 2003. If I recall correctly, even MS Word's spell checker wasn't developed in house, but the tech was originally licensed from Houghton-Mifflin in the early-to-mid-90s. I believe Word 7.0 had it, and possibly earlier versions, but it was still a "fairly new thing" in the early-to-mid-90s in the desktop space.
he went and got it all done up at the all night printer real fancy, it was his baby, but no he's not going to go through the pain of running a spellchecker, he's still a man dangit!
on edit: the hippy night guy at the printer place seems literate, he read it, but guess what - he has the same silly spelling errors as Jerry!
But yeah, the typo are likely unintentional by Crowe - in the end this is just a prop, and as I mentioned automated spellcheckers were annoying back then.