Fratzog
Old Man with a Hat
The 2 sheets for my 70 Polara were much the same condition as you describe. I took them in and had them laminated and now keep them in a binder with the rest of the original documentation. Done.
There are a few minor holes in the sheet. But dirt is by far the biggest code-blocker. There may be a few codes lost in the few holes, but I've already written those off as un-recoverable unless by some chance I were to find a 2nd sheet.
A lot of what you want to accomplish can be done simply by reverse engineering the sheet and/or comparing to other undamaged sheets.
Codes follow codes. if you see something in one place, i.e. a sales code, you will find the assembly code to match. The reverse is also true; if you find an assembly code, you'll know the sales code. Blanked out color codes are also easy to reverse engineer. Certain coded parts such as engine, carb, choke, transmission, pinion, rear springs and torsion bars, will, likely, be the same on similar sheets so that's an easy fix.
If you have a, pretty much, intact sheet but simply dirty or torn in places, you can probably determine most of what you want to know. If the sheet is missing huge hunks or completely obliterated portions, it becomes much harder to figure out. This is not lost cause. It's just a matter of knowing what you have to start and where to go from there.
I would not try to get a reproduction sheet until I know what should be on it. Do not trust the company to know what should be on your sheet. Their goal is to sell sheets; not provide accurate sheets and decoding.