EXCEL double IF statement with VLOOKUP - Handing Error on second IF statement

Basically, I have a double IF statement to check whether a certain value exists within the first list and if it's false then check a second list. Then if the value doesn't exists in the second list then I should know that the value doesn't exists in either list.

However, I'm having trouble with understanding in the particular scenario that the value doesn't exists in both list, why does my second false statement not work? I get #N/A for the value of 11.

I know I could use IFERROR, but I wanted to know the thought process of why it doesn't work!