Games : Book of Revelations doesn't work

According to the Binding of Isaac Rebirth wiki:

If The Book of Revelations is used at least once in a map, a Harbinger will replace the normal level boss.

I've found Book of Revelations in a Library Room in Basement 1 after defeating Pin boss. So I moved to Basement 2 in order to activate the book and make my next boss Famine. In theory.

The fact is that I found Larry as Basement 2 boss. How is this possible? I mean, the book should replace my next boss with a Harbinger. Why not this time?

Meat Boy and Bandage Girl achievements are driving me nuts...