The Soul Urge is the sum of the vowels of the full birth name, and the whole position rests on being able to say which letters those are. In English that is not a settled question, and the numerological literature does not settle it either.
Y is the standing case. In Yvette it behaves as a consonant, in Emily as a vowel, and in Bryan the sources this atlas cites for the chart give different rulings. The usual rule of thumb, that Y counts as a vowel when the syllable contains no other, is workable but is not applied consistently and is not derived from anything in the system. W raises the same question in Bowen and Shaw. Because moving a letter between the two columns changes both the Soul Urge and the Personality while leaving the Expression untouched, the disagreement shows up as two practitioners reading the same person differently.
Underneath sits a category error the system never confronts. Vowel and consonant are classes of sound, and the chart applies them to letters. English spelling drifted away from English pronunciation centuries ago, so silent letters are counted and sounds without letters are not. The e at the end of a name is worth five whether or not anyone says it.
Names written in another script have no vowels to count until someone romanises them, and competing romanisations give different totals for a name that has not changed. For a system that claims to read something interior and given, that is a large amount of weight resting on an orthographic accident.