Most (if not all) of the statements about BAP causing issues with daylilies are not based on objective evidence - most are hearsay as well.
Many gardeners know that if they have a plant (not a daylily - but any garden plant) that is growing with a single stem that "pinching" the growing tip will cause the plant to become bushier. That is usually considered a good result, although not necessarily if one is trying to produce large exhibition flowers perhaps. In any case what the gardener is doing by pinching (removing) the stem's growing tip is causing more growing points to start growing where there are (or were) leaves on the stem. There are axillary buds in those locations and pinching the stem's growing point changes the plant hormones so those axillary buds sprout. The plant will develop many stems.
In daylilies the stem is the crown (a condensed stem) which produces a fan of leaves and BAP is used to change the hormones in a similar way to pinching the growing point. The effect is to make the axillary buds on the crown sprout into new fans. Now if you make enough new fans from a single crown then they may be small. The more new fans the crown makes then the smaller each fan will be. That by itself may affect the survival of fans - that is their size. However, a similar thing can be done by taking a crown and cutting it into pieces. Each piece will likely sprout a new fan (until the pieces are too small). If one continually/repeatedly cuts a crown or continually treats a crown with BAP then the later in the season it becomes. So the fans become smaller and the amount of time for them to grow, produce and store resources for winter becomes less.
There are many factors involved and little or no factual objective evidence (data) that can be used to make objective comparisons about any possible effects of BAP versus crown/fan size by itself.
