No it doesn't. Most of the creatures in that class have, in fact, not been mentioned by you or anyone else.

If one of dem monsters exists, that would be evidence that more of dem monsters exist.

Realize then that a conclusion of "one of those monsters exists" is just assigning a high probability. It follows that just increasing the probability of "one of those monsters exists" also increases the probability ýou'd assign to more monsters of its class existing. It's a continuous updating relationship, there's no discontinuous jump in the belief in other monsters of the class which only occurs once you're sure that one of them exists.

Compare this to seeing an alien-engineered kaiju and then being less surprised at Godzilla (even if that's only in a neighboring class).