Just out of curiosity, I am wondering what is the standard policy of Hyatt.

Say, I make a paid reservation for two people on a regular room that accommodates two people.

If I use a Diamond suite upgrade certificate to upgrade the said room to a suite that accommodates four people, now I can bring four people, right?

In this case, can a property charge extra fees for third and fourth persons?

The reason I am asking this is that I encountered this "additional-fee-please" situation at one of the Hyatt properties in Japan.

"Staying at Regency Suite Twin & Tatami:
Room rate of 24220 JPY with Diamond Suite Upgrade
Additional charge of Futon 8700 JPY x 2 = 17400 JPY
This can accommodate 4 people in one room."

Is this typical with other Hyatt properties?

Thanks.