Tropicallvr

December seems the best month to buy seeds, since that is when most of the fresh seeds come on the market. Keep an eye on rare palm seeds web site since they are usually the first place to get new seeds.

1walaky- here's an anwser to your question,

Banana seeds(Ensete, Musa) aren't like most other seeds. If you crack one open you'll find a white starchy substance that is dry. This allows a seed to be viable for many years. In my opinion a banana seed can be viable until it discentigrates, is cooked(on heat mat or in sun), frozen(not sure but there has to be a minimum), or inside gets wet and molds/rots.
I have been able to germinate Musa balbisiana that barely had any black coating on the outside(down to paper thin membrane), because it was so old. I wouldn't give up on seeds for years, unless they are hollow, cooked(white starch turns yellowish), or have bugs/gnats which can spread.
Also some species seed seems to handle cold temps, such as Mussella lasiocarpa(golden lotus), which germinated for me after 2 months in the fridge.