New construction is famous for planting the landscape very tightly so it looks really nice right off the bat. Then it would have to be maintained soon or grow too big.
I'll see if I can find some info on the Clethra. I know what it is but haven't owned one.
I found a table of shrub pruning information from University of Virginia and will include the link below. This one says it will flower on new growth. If that doesn't seem to work for you, I would suggest you'll have to study the bush. Maybe put a few twist-ties on some stems this spring and then watch to see where you have flowers if any? I think Clethra is somewhat shade tolerant but sometimes too much shade is a reason for less flowering.