Dwarf is the same in that regard as regular fescue. I was noticing the
percentages you listed and am left wondering why this sod has fescue in
it to begin with. With 95% KB, it would seem to me that it would be
pointless to have 5% dwarf fescue, as it would be so overwhelmed by the
KB that it really wouldn't be doing much at all. Most mixes are done
to give a more balanced lawn that can then survive and look half way
decent when affected by diseases that hit one species, but not the
other.

As regarding the sod filling in, did you do a good fall fertilization?
Normally, I'd wait to put fertilizer down until its time to do the
pre-emergent crabgrass control at the same time, however with a new
lawn, I would do an early spring fertilization too, probably with a
starter fertilizer, as that is formulated to promote more root growth,
rather than quick greening with just nitrogen.