Early in 69 there were a couple of other casting number possibilities, but the most common ends in 512, which carried over into the 70 454's and up into 71 also. Obviously this number is 72 or newer.
For future reference, here's a couple of things you might keep in mind: They've all got casting dates somewhere. The earlier 69's and older had them down on the side of the block roughly in the area of the front of the starter. Sometime in the year they moved them up on the bellhousing flange of the block, kinda down behind the distributor, off to the right side. These numbers are easy to read, hard to fake, and cut through a lot of the original engine BS when compared to the build date of the car. They would run in a sequence such as A 10 9, meaning January 10th of 69, B - Feb, C - March, etc.
Incidentally, when describing the side of a block (or anything else on the car) its from a sitting in the seat perspective. The passenger side is always referred to as the right side. Chevy didn't do any pads for engine stamps on the left side.
Just because the car has a later engine doesn't necessarily mean you should pass on it if it's a good car otherwise. There are a number of telltale signs to indicate that it's an original factory big block car.
