Tag restrictions on arrival
Reconstruction later rarely works.
Not through fraud. Through restricted money spent on payroll because nobody was tracking it.
Nonprofit accounting has one feature that business accounting does not: some of the money arrives with conditions. A grant for a specific programme cannot cover general payroll, and an organisation that pools everything into one account will eventually spend it that way without a single person intending to.
Reconstructing restrictions after the fact is close to impossible. Tagging each gift as it arrives costs nothing; working out eighteen months later which dollars were restricted costs a funder relationship and sometimes a repayment.
The other avoidable failure is the board pack. Treasurers are usually volunteers with day jobs, and a report full of unexplained variances gives a board no way to govern. Short, consistent, and explained to the treasurer beforehand is what turns reporting into oversight.
Reconstruction later rarely works.
A board pack nobody understands is not oversight.
Audits need an independent firm.
Free, with an honest view of what steadying them would take.