This is not true.
If you have the first 11 words of 12 word BIP39 seed phrase, 1/16 of the words will give a valid seed phrase if they are used as the 12th word, but this doesn't mean any subsequent 16 words will include 1 word that will give you a valid seed phrase.
For example, it's possible that none of the first 16 words can be used as the 12th word.

This is not true.
If you have the first 11 words of 12 word BIP39 seed phrase, 1/16 of the words will give a valid seed phrase if they are used as the 12th word, but this doesn't mean any subsequent 16 words will include 1 word that will give you a valid seed phrase.