Not enough data. There are 45 vices I've gotten, 3 without dates, 3 gaps of 5 or more years that matter.
The earliest date is 4/45. since they started production at least by 1941 (that is the incorporation year) that's one gap that supports that the dates were the expiration date from the start... (there are three vises clearly early models, that have no dates...)
Leaving the Cadets out of the picture for dates (they had a 3 year Gaur.) there is a 7 year date gap that cannot be explained.
Regular Wilton';s had "Exp" or a variant from 60 -62. For Cadet's there are examples from 55-66.
Personally I still think the dates were expired dates from the get go, but nothing yet to confirm it...