Hi Leo,
May be you can use Time Dependent Hierarchies?
In general the rule is simple:
If you use same parent in different hierarchies - then this parent is required to have same base members in both hierarchies!
Vadim
P.S. "At a later date a new account appears in PARENTH1 but I dont want it showing in PARENTH2 or it could be under a NOTASSIGNED node." - not possible!!!!