Newbie needs help decoding!

Dollar Dude said

Numbers matching is used in different ways by different people.
I refer to the usage that indicates that the codes and dates stamped on the major components of a car should match available records, showing the car most likely has its original major components. The 1968 stamping of engine blocks with partial VINs was not the beginning of the use of the phrase but is one more item to check.
Haggerty Insurance has a good article on the subject.

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Numbers matching and date codes are two different animals.

Charrlie_S explained it correctly.

Even IF the date codes are correct, it still doesn't tell you that the engine is the one that came in that car, only that it was produced in that time frame.

Numbers matching will have VIN#'s on the engine that correlate to the VIN# on the car, therefore you know that particular engine came in that car off the line.