The thing is, if your sittin on considerable inventory of old weld material it might make sense to consider how much damage they may have been exposed to, and even run a couple of tests, if you so wish, such as tensiles, bends, RT, or UT.
At one plant I worked at they had accumulated well over $250,000 of unused weld material by the time I arrived (310, 316, 317, NiCrMo's, NiCrFe's, NiCu's, etc.-not all of it SMAW of course-high alloys ain't cheap). Some of it with Nuke certs. You can bet that before we went tossing it in the can we considered carefully the alloys, the possible damage, and the application. Some we tossed. Some we used. Some we gave to the local apprenticeship school. Some we sold to secondary markets.
Talking of failures is unduly ominous considering there is so little, if any, evidence of failures due to aged coatings.
I believe its safe to say that you will witness a deterioration in arc characteristics long before a deterioration in weld properties.
Now this certainly isn't an advocacy of going on ahead and welding with a electrode that has a coating that looks like mud. Just a statement of not, by default, tossing electrodes because they are old.