There is a difference between interfacing and ( applique fusibles) interfacing is a ( cloth like) product used to add body or keep fabrics from stretching....heavy weights used in collars, cuffs, stiff items; lightweights used behind knits, silks, etc to keep them stable.
Fusibles like steam a seam, heat n bond, wonder under are totally different products.
ive had wonder under and heat n bond that has lasted for years & is still usable. I would imagine that it depends on how it is stored. Protect it from humidity & it should last until you use it.