I'm convinced it should be "stitch", thanks to
Ribbedroof . There's factory-provided evidence to support it. The biggest variance I've seen with different window stickers is abbreviations. Some squeeze down the word by taking out vowels, others just cut off the word to make it fit.
If it is a typo, I would expect it to be on many, if not all, the window stickers unless and until that someone found the problem. GM didn't just set up the printing machine to make just one window sticker.
I know you aren't going to want to hear this, but another thing I'm convinced of is that these are repros where PHS did the typo. I'm not saying this to stir the pot or pi$$ anyone off. I'm just pointing to the truth.
Since you mentioned that PHS did the window sticker, PHS never provided "original" printed-by-GM window stickers. And if they were original, they likely would be a different color than bright white like it was printed yesterday. I'd expect a 40 year-old document that GM didn't really care about but only done because of Federal law to have a bit of yellowing to it. Plus they're missing the part number of the window sticker that's somewhere on the bottom margin of an original, either down the side or bottom in the corner.
This just dawned on me to look over the whole window sticker to find those anomalies. When I was researching window stickers, I ran across many people that were doing it. Some were doing it right and eerily accurate, some weren't. These folks typically make them off an invoice and according to Mike Noun (who makes very accurate Pontiac Firebird window stickers) PHS did a decent job, but has areas that aren't correct. Unfortunately, PHS isn't going to fix it, because they got out of the window sticker reproduction supplier service about 6 years ago.
To borrow Mike's Firebird picture to show differences...