What is not working exactly? AT("revJ", "855956-401 revJ2") give me 12, which is the correct starting position of "revJ"

>I am tring to find a way to check for a string within a string but what I have came uo with is strill not working every time.
>
>I am using the AT() function but this fails if my:
>
>search expression is revJ
>and searched expression is 855956-401 revJ2
>
>J and J2 are two different revision levels.
>
>Sometimes searched expression can be more complex like:
>855965-401 revJ2, 855965-403 revJ2, 855965-405 revJ2