I think some vendors rely on giving the rhizomes more nitrogen to produce more leaves and less blooms if they need an iris to multiply for sales stock.
If a healthy rhizome, that has been taken care of, and given proper nutrients and water throughout the previous year, is sold, the buyer can expect a higher percentage of bloom than a rhizome that has been out of the ground for an extended period of time. Whether this is due to the vendor digging and packaging them a week later, shipping issues occurring or perhaps not planted immediately by the receiver does not matter. The rhizome (and I may be wrong, I was once before) is not a bulb but an underground stem. It does survive if not planted immediately but it is not like a spring flowering bulb that stores bloom energy and goes completely dormant. When it is out of the ground and has used a lot of the moisture in the rhizome to survive and the roots and leaves begin to dry up it has used up its bloom energy for the following spring. Some irises are finicky but I think more are blamed when perhaps their needs were not met. IMHO
