Well, yes in practice, but not in theory. In theory a variety referred to as an IBL should be consistent in the expression of more or less all of the primary characteristics of value in a commercial crop - from stature to maturity period, disease resistance, leaf and fruit appearance, etc. “Peas in a pod” as Oldtimer says.
But you are right in that there are a lot of “IBLs” sold at seed shops that shouldn’t be labeled as such. Inbred lines need several generations of backcrossing by a skilled breeder to fix traits and cull out-of-character individuals. Most breeders don’t have the discipline to see a project through to IBL, and seed buyers don’t really reward the effort, because who cares if a strain is IBL or F1 if you are only going to plant 10 seeds and grow most strains once? If you like a strain you clone your best girl and you’re done.
IBLs are more important to breeders and the future’s large commercial ops, where Blue Dream and Bubba Kush will be planted like corn in Kansas, and harvested the same way. In those operations, having ten thousand seeds that grow exactly alike will be far more valuable.
-b420