Addendum: Some modern strains don't drop spores easily. PE-type strains that I have been growing are like this. You gotta do some digging up in them gills with a qtip if you want to attempt to collect any spores if there are any to collect at all.

This varies from strain to strain, of course. For example, the veils break super early on Mac Galactic even though they have a long way to grow. The "feels like a marshmallow" test can be better in cases like this.