(Question)
I have several packets in a tin of seeds, some of which were quite expensive. I hate to throw them away. Some are three to four years old.
Any guidelines?
(Answer)
Seeds have their own germination rate, viability and requirements depending on the type of plants they are from, so without knowing what seeds you actually have, I would only be guessing as to their viability after 3 or 4 years.
The Toronto Master Gardeners have a Guide, “Growing from Seed”, which may be of use to you for general information and instructions on growing plants from seed, see the link below.
I would suggest you give them a try and see what happens, you may be pleasantly surprised.