What is the shelf life of unopened jarred hollandaise?
So, it's in a glass jar? So it's pretty much mayonnaise made with butter instead of oil. As long as the vacuum seal is good, and the lid pops when you open it, you should be good. Modern shelf-stable products should last years in proper storage. The worst thing that could happen is the fat could become rancid, which is an aesthetic problem, not a safety problem. Taste it, and if you think it tastes good, go ahead and use it.

If the lid doesn't pop from releasing the vacuum, or it's pressurized and hisses like a bottle of soda, or there's discoloration/mold, or it smells weird, then discard it.