[tor-relays] What are the exact requirements for HSDir flag?

Hello, and Happy New Year!

I have a question regarding the HSDir flag.

According to dir-spec.txt :

"A router is a v2 hidden service directory if it stores and serves v2 hidden service descriptors, has the Stable and Fast flag, and the authority believes that it's been up for at least 96 hours (or the current value of MinUptimeHidServDirectoryV2)."

However, if you browse the consensuses, you will find a lot of relays that meet the requirements above, but doesn't have HSDir. You will also notice that almost every relay with HSDir is also a conventional v2 directory mirror (e.g. with active DirPort).

Is there any non-documented requirement, like minimum bandwidth or something?