There may not have been any. There's some evidence that catnip response is not just context-sensitive in that the same cat a few days apart might respond differ

There may not have been any. There's some evidence that catnip response is not just context-sensitive in that the same cat a few days apart might respond differently, but also that catnip insensitivity might change over the span of a few years. Like most things about catnip, any reason for this is a mystery.