Any calcium can bind with fluoride when there is water present. Without water, NaF stays as NaF rather than breaking apart into Na and F.  In FluoriMax Varnish (and all other varnishes), there is no water present so the NaF and whatever calcium source is present will not interact while in the package.  Only when the varnish is placed in the mouth does water get into the mix allowing the F and Ca to interact.  This is exactly where you want these reactions to take place.