Something odd is that these bulbs receive year round rainfall. The seed is shed in late spring and remains in the ground where it receives rainfall and dew every night during the whole summer dormancy period. When nights become cooler in autumn, every seed germinates in an impressive "lawn". It is normal that people store seed from this part of the world in paper packets until sowing time, like we do with Mexican, Cape, Mediterranean, etc. species, but this way many embryos die off. This problem is very serious with South American tigridioids. Of course in cool/cold climates the embryos take longer to die.
What to do then? The best procedure is to sow upon receipt and place the pot with seed in some shady corner where they receive a good soaking every fortnight or so, broadly speaking. In any case, the seed must nor dessicate.
Ipheion uniflorum and others' do not require stratification. The seed respond readily to cool nights as said above. Germination takes place in autumn.