In addition to the casting date of the block, you should always also consider the engine final assembly date as well, especially since that number would be visible . As mentioned already, block casting dates can be months and in some cases a couple years prior to the cars SPD (although generally "most" fall within 4-6 weeks)however, the engines final assembly date is "usually" pretty tight against the SPD, usually 7 -10 days , but can of course be longer, or in some cases post date the cars "scheduled" production date , because the car did not get built on its actual SPD .

Greg