I agree with Seedfork, I believe pre-emergent only effects seed germination. I have found newly planted bulbs typically are a bit later to bloom and develop that first spring, so the foliage may have been right at the stage where it was building up food reserves when the lawn was mowed. I suspect the foliage is doing its job earlier this year, and will have restored the bulbs before mowing this time around. Although I do find it a little odd that there wasn't at least a stray bloom here and there.
