Math was NEVER my strong suit. Being obsessed with chicken colour genetics is, perhaps, helping but math still isn't my thing. Is it possible to be Bl/Bl and Lav/Lav? Conceivably, you could take two E/E Bl/Bl Lav/lav's and end up with Bl/Bl Lav/Lav? What would that look like? Probably just like regular splash? Or would that then be a self-blue base with splashes ????
The problem is not so much math but written gene abbreviations uppercase (=Dominant) and lowercase (=recessive) letters to count with.
Indeed every combinations of (color) genes is possible because they have different loci (=place on the chromosome), so also E/E Bl/Bl lav/lav which should be a Black (E/E) diluted with 2 dosis of Blue (Bl/BL) also called Splash = some kind of dirty white with splaches which with 2 dosis of lavender (lav/lav) which would diluted these splashes to light gray (=lavender or in US called "self-blue") evenetually looking as ... almost white I suppose !!!
An other better known example is a rooster "lavender cuckoo" => E/E B/B lav/lav ;-)