There is a difference between layer managers where trace impedances, board thicknesses, etc. can be calculated
and "real" planners that take possible via spans over several layers, blind and buried as well as maintain tables for dielectric
thicknesses and baking combinations into account. The best thing to do after realizing that a complex multi-layer board is needed
is to contact the board manufacturing factory and ask "What are your most popular build-ups" in terms of dielectric and prepreg
availaibility, plating procedures and the combination of baking in several steps (intenal layer via spans). When I deal with
10 or more layers, it is a must. I also get recommendations regarding the materials and the qualities that moves more often.
This can be important, since prepregs stiffens as they age which affects trace impedances if inner traces are routed with a prepreg as
one of the dielectric layers.