dnd 3.5e – How many epic spell seeds can you know?

It does not count as a spell

Seeds are used only during the development part of creating an epic spell and have no effect on how many epic spells you may prepare or cast, though they are fundamental part of creating an epic spell or spells.

As far as I can tell (checking here and more specifically here) there’s no actual ‘seeds known’; seeds are not learned, simply used. With that in mind there may be a contradicting source from outside of the SRD, and certain epic prestige classes interact with specific seeds (for example, the Netherese Arcanist from the Player’s Guide to Faerun)