Listing occupation is mandatory on 460s
I was wrong about there not being penalties for omitting occupation from 460 forms. This is from the list of instructions issued by the FPPC to help candidates fill out their 460s:
Contributions from Individuals: When itemizing a contribution from an individual, also disclose the contributor’s occupation and the name of his or her employer. If the contributor is self-employed, provide the name of his or her business. If the contributor is not employed, enter “none.” It is not necessary to enter occupation and employer information for other types of contributors (such as business entities). New Requirement (All Committees): A contribution of $100 or more must be returned to the contributor within 60 days if the contributor’s address, occupation and employer information is not obtained.So if we are talking about individuals, they always have to provide an occupation, even if they are self employed (name of their business). Business entities and organizations, of course, have no occupation to list. But it sounds like anything more than $100 received from an individual without "obtaining" their occupation has to be returned.
That term "obtained" sounds to me like a loophole. It could be interpreted thus: I "obtained" the contributor's occupation when he or she gave me the money, I just didn't "list" it. If the official is called on it, he or she can simply show their books, note that they knew the occupation of the donor but forgot to list it, and then amend their 460 forms.