The picture shown is horrible for determining much of anything.
Are you absolutely sure it is an E?
Do you see any visible signs of what may be a repair of the block?
I can come up with a couple of reasons a block would sit for 11 months before being built.
1. A repair needed to be performed or
2. It was uncycled inventory (by uncycled I mean a FIFO inventory system was not being employed.)
That being said lets talk about the block, ... the deck looks to have a decent amount of rust pitting, make sure the pitting is consistent across the stamping, in other words makes sure there are pits in the stamp character impressions and they match the rest of the pitting.
As far as an assembly date being too early, I do not believe there are too many norms associated with 67 L78 production, there were too few built in the 4 months they were produced in order to draw many meaningful conclusions.
Bergy worked at Tonowanda he or JohnZ may be able to elaborate on the inventory procedures and whether it is possible and if so, the probability of it happening.