This was before the SaaS days.

On-prem, single company who issued invoices to customers.

When there was an audit the government could ask to see invoices in a certain range. If some of them were missing, what does that mean? Paid under the table?

My wife worked at a place where they did manual PDFs, but there they had a tool to change properties of a PDF to change the creation time / last editing time, for when 'modifications' were needed.

And this reminds me of the other post here where some people assume cash means shady. Definitely the case there.