I think the 'guidelines' are general rules that vary widely with the use of the item. If you're careful with your e/s (keep lids closed when not in use, store away from heat and humidity, clean brushes regularly and/or *don't* share your stuff etc... they'll last much longer. An occasional spritz with alcohol (99% since it has less water and will evaporate better and damage less) wouldn't hurt either if you're in doubt.

I don't have the heart to toss e/s that are old but look/smell/perform well. I think hygiene and low humidity are key to a long life of an e/s.