I have been germinating seeds for about a year now, and in my experience the packaging date would bring a world of change at the time of planting our beloved seeds.
I had problems with a few seed packs, Mephisto 3Bears OG (they sent repos), Crockett's Double Tangie Banana (0 out of 12), Humboldt's Blue Dream Auto (0 out of 3), GreenHouse's Super Lemon Haze (2 out of 6), CannaBioGen's Punto Rojo (2 out of 7, sent repos but got seized), GreenHouse's Green-O-Matic (0 out of 3), and also the freenies i got with my every purchase, i probably germinated 20 seeds in their unique solo baggies they come, but out of those i harvested only three seeds. Check the thread for the 16oz cup we had and you'll see.
Having dates on seed packs would encourage prices to be more competitive in order to get rid of them quicker, no one would buy old seeds, also if the seeds are fresh you may find out about what happened if a seed pack doesn't give results, irradiation, extreme heat, adverse conditions and such.
IMHO, we are being cheated by BIG seed banks into buying very old seeds but they don't tell us about it.
DO NOT BUY SEEDS COS' OF THE FREEBIES YOU ARE GETTING. (They will not germinate)