Right(len(a1)-etc..
equates to right(25-18) for the first entry.
25-18 = 7, there is no second argument for the RIGHT function so it defaults to 1 character, resulting in mid(a1,find("ST",a1,7)
St-01 f is 7 characters long.
Try
=IF(ISNUMBER(FIND("ST",A1)),MID(A1,FIND("ST",A1),FIND(" for",A1,FIND("ST",A1))-FIND("ST",A1)),"")