This used to confuse me: don't co-op rules like this distort the value of the firm? But then I realized that I was missing the big picture: the ownership of the firm isn't valued! Worker-owners own a portion of the revenue during their time as worker-owners, and there is no need to put a price on the expected future revenue or profit of the company.
It's not co-ops that distort the value of the firm, it's that permanent ownership necessitates complicated and opinionated financial/statistical reasoning to put a number on what is fundamentally a weird social relation.