Split and recessive are not the same. Split means the bird only carries one copy of the gene; for a recessive gene, it does not show when split. With lavender, a split is Lav+/lav, whereas a bird showing lavender is lav/lav. A bird who is Lav+/Lav+ is also not split, but you cannot tell the difference between it and a split. You can only know because of breeding: either one parent was pure for lavender (and therefore showed it) or bred to a lavender or another split produced chicks showing lavender.