When I purchased ,my car , I was told that it was a number matching engine, I spoke to 3 of the 4 previous owners, the only person not contacted was the original owner who is no longer alive. Anyway I  sent  for GM documentation  just recently and  the engine # came back as 816632634.  I checked the block, and the number on the block is 816633634. How are these numbers decoded? Do they have to match exactly? As you can see they are very similar only one digit different. I thought maybe a typo error from GM? 

                                                                         Thanks in advance for any info.