How Many Investors Before Spreadsheets Become Risky?

The key is to not have any specific number of investors beyond which spreadsheets fail. The level of complexity trumps number of investors.
Ten investors can be challenging where the commitment, side letter terms, entities, and reporting are different.
Fifty investors are manageable where the process is seamless and data has been managed properly.
The real indicator would be how people behave within the process: duplicate entry, manual reconciliations, unmanaged versions, late deadlines, and investor-specific rules that are not documented.
That is when the discussion is not whether spreadsheets open anymore; the discussion is about whether the process has become reliable and reviewable.
What was the first indicator that you had outgrown your initial process?