You're correct.

Re co-ops, on p. 585-6 you'll find: "The project’s operating budget must...provide for adequate replacement and operating reserves."

And on p. 591: "The co-op corporation must maintain replacement and operating reserves."

Language in the most current Fannie Mae guide is the same; no 10% or other specific requirement is mentioned.

I’ve not heard of any co-op building being blacklisted by lenders due to non-compliance with Fannie Mae reserve rules…just condos.

If anyone is aware of a co-op mortgage denial where this rule has been invoked, please post details here.