Bergeron wore his junior number into pro hockey, but it seems that sometime around the Krejci era it became fashionable for guys to want to keep their camp numbers when they became regulars. Krejci was issued 23 in Providence, 46 in Boston. 23 was available when he became an NHL regular but he stuck with 46. Lucic, on the other hand, went from 62 to 17.
Neely was issued 8 when acquired in 1986 and asked for 12 for Stan Smyl, whom he grew up idolizing in Vancouver. But Harry Sinden liked him better in 8, so it was. Randy Burridge was in the minors that season and did not yet solidify 12 as his number.
BTW: Niklas Svedberg wore 1 in Providence, wears 72 with Boston.
So 6, 10, 13, 14, 16, 19, 21, 22, 26, 28 and 29 are all <30 numbers available.
10 should be retired for Bill Cowley.