You can structure a Regex search so that the string you are looking for does not appear in the beginning, middle, or end of another string of numbers and/or letters. For example when we want to search for a 4 digit number, we enter the search: [0-9]{4} - any four digit sequences of the digits 0 through 9. In order to exclude instances of a four digit number such 1977881 or AA1122ZZ, we precede and follow this search with [^0-9a-zA-z].

[^0-9a-zA-z][0-9]{4}[^0-9a-zA-z]

See this example in NotePad ++