(Hard) - SerDes Magic Number - Startup

A startup asked me the following question during a verification interview after I mentioned I work on SerDes products….

In a SerDes, magic numbers are transmitted by TX and received by RX. These can be referred to as k-codes in certain serial protocols. The RX declares that it has “locked” to the TX if it receives and decodes the correct sequence of magic numbers. However, in such protocols, video data or other types of data may also be transmitted from TX to RX. How does the protocol ensure the data itself (e.g. video data) is not decoded as a sequence of magic numbers, falsely declaring lock?