The $352 million on ad spending is a drop in the bucket. It doesn’t include other expenditures (staff, as you mention, but also consulting, transportation…). Nor does it include money Bloomberg has given other candidates and committees ($65,188,915 in 2018 alone to his PAC Independence USA, which redistributes the money to other candidates and committees), and which can obligate the recipients to return the favor with endorsements, support in interviews, etc. On top of that, Bloomberg contributes to other SuperPACs which aren’t required to disclose donors or amounts. This dark money is in the form of independent expenditures, which means if you visit the recipient’s campaign committee FEC filing, you won’t see the donation. (My elaboration on the process here: https://medium.com/@slhale/mayor-mike-doesnt-need-your-stinkin-contributions-e813a1257218 )