Numerologists hold that a number attached to a person, through a date that was not chosen or a name that mostly was not, expresses something durable about temperament and about the shape of a life. Almost nobody in the practice offers a mechanism, and the more careful practitioners describe the numbers as a symbolic vocabulary for self-examination rather than as a causal influence.
The disagreements inside the practice are real and are not resolved by any authority, because there is none.
Which name to use is the first. Birth certificate name, current legal name, married name, chosen name and nickname all yield different figures, and schools differ over which is definitive; some read several and treat the differences as meaningful, which is a convenient position and is acknowledged as such by critics inside the field.
Which chart to use is the second. Pythagorean and Chaldean assignments give different values for the same letters, and both are in wide commercial use. There is no principled way to choose between them.
Master numbers are the third: whether 11, 22 and 33 should be held back at all, and whether the practice of doing so is old or was introduced with the modern system.
And transliteration is the fourth, and the most awkward. A name written in Arabic, Devanagari, Cyrillic, Hebrew or Chinese has no letters in the chart at all, and the practice's answer is to romanise, which means the number depends on a transliteration convention.
None of these are hidden. They are argued about in the numerological literature itself, and a practitioner who says which system they are using and why is being straightforward about a genuinely unsettled method.