I've used the registered bloom time to check out the plants and look for forming scapes, but I'm not very confident that it's going to be completely reliable. In the time I've grown them 'Primal Scream' which is registered as 'ML' always starts bloom before 'Selma Longlegs' which is 'EM'. They were planted in identical containers at the same time and are located side by side, so they get everything the same at the same time - water, fertilize, sun.
On those I've had long enough to have overwintered outside before, I'm using the dates they started blooming here in 2015 which, in theory, should be more reliable. Most of those started in early to mid June, so there's plenty of time, but a few started in May from early to the end and those are the ones I keep watching thinking they should start scaping any day
. Mostly I think I'm just being impatient. I think I found one today that was new last summer and began blooming in July. I expect some of that. It was from a northern supplier and bloom last year was geared to the northern winter, not mine.
The seedling showing the scape came from an E pod parent, but the three possible pollen parents were EE, M, and ML. I'm not sure whether seedlings even correspond to their future timing anyway on initial bloom.