Question on chip date code

I am looking at a chip that is causing me confusing with regards to its actual date code. The chip is labeled thusly: (logo) /718 DM74157N 9322 (logo) looks something like this: /\/ /\/ ...which probably makes it National Semiconductor. My first instinct is to guess that its date code is 9322. However, it does not fit within the context of the rest of the board, which is 1976. They are definitely not original, as the board calls for a 74257 but the 74157 has been put in its place with the addition of a capacitor across +5 and ground. Is it possible that the date code is actually "/718", and what I am seeing as a slash is actually what remains of a '7' that wasn't printed correctly?

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