IN GENERAL there was a wide range of acceptable dates, as mentioned most distributors were built in batches. The date that is critical is that the distributor date preceeded the engine assembly date. With shipping time a consideration I would think the closest to the engines assembly date you will likely see a distributor assembly date would be around 2 weeks prior, but most I've seen were a month or 3 earlier. When going the other direction, I have seen A LOT of distributors assembled over a year prior to engine assembly dates (for instance it's common for 71 Hemi's to have 1969 dated distributors).