The date traditionally assigned to them is 1948-52. I have no idea why; I do not think it is right. For example, Jean Beliveau, the great Habs player, has two cards in the set. The portrait shows a very Young Beliveau in a Montreal sweater while the second card shows him full length.
He played two games in 1950 then went back to the juniors until 1952, when he played three games. It wasn’t until 1953 that he stuck with the Habs. I doubt either card predates 1953. The full length image shows him with a captain’s “C” on his sweater. I don’t think he made even temporary captain with basically no experience and so many veteran HOFers on the team. My guess is that the Beliveau cards are mid-1950s and that the Canadian 'Exhibit' cards do not match the dates that early cataloguers assigned to them.
The Gordie Howe card is consistent with two other issues of the rookie era. Here is the 'Exhibit' Howe:
Here is a McCarthy postcard:
Looks to me like the same photo session at the least. Now here is the Parkhurst RC:
Very close even down to the mark on the stick between his hands. My best guess is that the Exhibit, the McCarthy and the Parkie are about the same age.