Whitehead wrote before analytic philosophy and symbolic logic were too well advanced although he and Russell did a lot with Principia Mathematica. Truth theory (there are several) does yield whole truths. Disquotation and Correspondence theories for example, postulate the existence or non-existence of something, perhaps in a list. It either exists or does not exist. Like binary computer logic of 0 and 1 the location either has a 0 or 1. Sure there are other logic modes and additional ways of saying that something is or is not, and in some instances there may be states that are potentially 0 and 1 simultaneously perhaps, in a different structure, yet Whitehead’s idea is probably pedagogical and referent to learning about reality and life generally- there is always more to things. Simplifying language and ideas so it is verifiable and meaningful and accurate using symbolic logic within an epistemology and ontology can allow one to find conditional whole truths.