Not to be smart, but of course they will deteriorate.
That said, a perfectly new, not-scratched, visually fine pressed disc can scan like any of the above (except for the disc with the score of 5). It would play fine for years to come, in most players that had a decent disc drive.
Or you could find that the disc was improperly bonded or something similar, and it wouldn't last long at all.
So check the disc for physical flaws. If all looks well, you have hopes of the discs being fine for years to come (similar to burned DVD media).
Your job is to make sure that the discs don't get any more scratched, since it was likely not deterioration* that caused the low quality in the first place.
*: (related to the manufacturing process and qualities of the used materials resulting in visual rot, etching away of the surface by oxidation, etc; anything not caused by improper handling)