Hi orchidd,
most seed packets are dated, but if they are not, I always take a marker and date my packages of seeds. I have lots of seeds and some are ten and eleven years old. I am going to plant some of those this year and see if they come up.
Lots of seeds will last for years. I've found that lots of herb seeds don't stay viable for very many years. If I get my act together, I have to get on the ball and order the rest of my seeds. I have sent out one order. I need to do a couple more.
Just keep planting these seeds.