Dan, I see it's time we had that talk about the Boletes and the Russulas (that's Birds &
Bees for those of you still stuck in the Animal Kingdom).
In the Fungal Kingdom, sex is much more logical than the Animal Kingdom. None of this growing up and puberty and something as ridiculous as "sexual maturity". Fungi can't be waiting around to grow and
then have sex, the environment might dry out and then they would have to go back to being spores again. Spores are ready to swap DNA as soon as they germinate, in fact, the sooner the better. As soon as the spore has come out of dormancy and extended a few cells of hyphae, it's party time! Time to pair up with the nearest available partner and compare DNAs, see what genetic variability can be introduced into the next generation.
So
the answer to your question is yes, new spores are always welcome. As soon as they germinate, they may have a gene that works particularly well for the piece of lignin they are sitting on. In that case, that gene is going to be very useful and that newly emerged piece of hyphae is going to be prime mating material. Its daughter cells will be in a good position to increase their representation in the colony.