It seems like size and even variety type might play as much a role as planting time and environment to determine if it will be a bulb or a round.
Germidour I planted outdoors in fall produced all rounds, same as january greenhouse. But Messidor in the greenhouse produced 7 small bulbs and 7 rounds - from bulbils! Thermidrome are all rounds. Just today I removed scapes from Early Purple and Tallinn outdoors, each group has one plant without a scape, which might be a round, and the rest bulbs. Early Purple in the greenhouse produced a half dozen rounds and eleven small bulbs, so perhaps a higher percentage of rounds compared to outdoors/fall. The do have quite a few cloves (7 or so) which makes the cloves quite small compared to the bigger rounds. I will be interested to compare what comes of planting these cloves vs the rounds.
The bulbs from Alexandra and Messidor have large enough cloves to grow up faster or as fast as the rounds, but we shall see! It will be fun to compare them.
And Kolkja Red Russian produced a couple of bulbs from the bulbils as well as a lot of large rounds, but to be fair the bulbs are smaller.