When I saw your question I checked my newer sources. All My books list one species B.d. melantona Since under the rules of clasification if there were no subspecies you would just have B.dendrophila dendrophila obviously there are more.
Mehrtens supplies the following list which may still be valid.
Boiga dendrophila
melantona
denrophila.....Java
annectens......Borneo
gemicincta.....Celebes
latisfasciata..Mindano-Phillippines
muticincta.....Palawan " "
divergens......Mindano " "
Frank
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"The luxury of not getting involved departed with the last lifeboat Skipper..."