The key is to have your alterations measured by the tailor -- not a sales person. If you are measured locally and the work is done in NYC, there could be some disconnect. I doubt BB Black Fleece has any unique construction that any competent local tailor could not handle.
I have purchased suits, sport coats, trousers, etc. from my local BB, Nordstroms, NM, Dillards, etc. that have needed alterations. I never have their house tailors do my alterations as I found a local tailor shop run by two great Chinese women who do amazing work, at reasonable prices and on time. I have been taking all my alterations to them for many years. They know me and how my clothes fit. If you can, find a local independent tailor and work with them. Results will be consistent no matter where you bought your clothes.