The correct 'term' is BwHoPL, meaning:
Being with Heart of Pure Light.
That is a general term to the beings we know to be PoHs, meaning -
Princess of Heart.
I think you see now why we'd use initials, as long as they be themselves.
Why differentiate, if the PoHs are BwHoPL?
Because we don't know them to be the same people. In the BBS trailers, they go after the BwHoPL to summon Kingdom Hearts, yet they don't call them Princesses, as they do in KH1 and onwards.
Many speculations arose due to this, amongst them the possibility of a BwHoPL being male (hi, Ven). This would no doubt require a 'change in staff' so we'd get the PoHs we were introduced to in KH1, but until further information is disclosed about the identities of the BwHoPL, showing them to be all 7 PoHs we know today, the more general term is used when dealing with BBS.