If they are noble, the beta will take over. Its creates a slightly harsher bitterness, but you can use them the same will little to no alpha adjustments.
^^^ This.
Personally I find that as long as the hops are properly stored (cold, no oxygen), all the calculators and data available tend to way over-estimate the loss of actual real-life bitterness from the hops. For example, some sources might say that X hop with 5% alpha will be reduced to 4% after 12 months. But if you assume this is correct and pump 4% into your homebrewing software, it tastes too bitter as if it still had about 4.7-4.8% alpha or something like that. It does degrade, but...... it's not so easy to pick it up, until several YEARS later. And even then, it doesn't lose as much as you think. That's been my experience. I've used hops that were 3-4 years old many many many times, and based on taste in the final beer, they really never seem to lose more than 1-2% alpha acids as calculated in software. If tested in a laboratory, then sure, maybe these beers have less IBUs. But then, what about beta acids? IBU tests don't look at beta at all; however, your mouth does! Beta stays around for a long long time and probably makes up for most of it.
That's my experience. I use lots of really old hops with great success. Don't use them for aroma in your IPAs. But for bittering? That's exactly where you SHOULD be using them!!