I've been involved in at least a dozen audits during Series B/C fundraising periods, the bulk of which included financial models with forward-looking quarterly forecasts backed up with prior-quarter actual results.
Accounting audit usually involves accountants/CFO going through how the accounting system accounts are structured, and how those accounts get turned into the three financial statements (cash flow, income statement, balance sheet). You might have a unique accounting scenario where large expenses can be amortized over several periods, and an auditor will check how that reporting schedule was produced to net out what everyone is looking at on the financial statements. Maybe there was an acquisition that didn't quite pan out and there's an impairment charge that had material differences. Maybe your business collects cash upfront but reports deferred revenue. Maybe your company offers a product warranty so there's a non-trivial accrual schedule to consolidate warranty liability.
I worked at a company that convinced the SEC that it generated revenues from its published content over a 5-year period, allowing it to amortize expenses over that revenue-generating period while front-loading revenues over the first 18 months. Eventually the SEC changed the rules and expenses were expected to be reported in proportion to revenues.
There's a lot of ways those numbers can be put together, with a lot of different rules for how cash, revenue, and loss can be represented and disclosed. The kinds of errors I've seen encountered are less Excel formula errors, and more fundamental issues with account structures and how numbers are being strung together to reach what is reported.
The impression I've received is that what matters during the audit process is not if there are mistakes and errors, but if they lead to material changes that alter the trajectory of any decisions being made.