Starrett does make some very good precision tools. Their framing squares are listed in their "jobsite and shop tools" section as opposed to precision tools and at the price I would not expect too much of them, The graduations are stamped, there is no listed accuracy and I would bet that those squares are sheared and deburred rather than machined to size. I would consider one a kit, like many tools, and expect to true it up with a file and center punch using the principles Mark alluded to.
If you want a really accurate large square (not a framing square) Starret makes one, and they charge a premium price for it.
https://www.starrett.com/metrology/p...Specifications Woodpeckers make a similar one with a claimed accuracy of about .001"/ft.
https://www.woodpeck.com/catalog/product_compare/ I don't know if anyone makes a traditional framing square with tighter standards then Lee Valley. The advantage of that design is that you can tweak it to reasonable accuracy, even after dropping it on the floor. I know someone who did that once.