Dude, you're just digging yourself a bigger hole. There is proof of dating, right on the cards themselves. ESCO made two team cards each year: the pennant winners in each league from the prior season (stopped in 1956). Here's the 1952 printing of the Yankees card:
Notice that it says "1951 World Champions"? Well, when did the Yankees become the 1951 champs? In October 1951. Here's the 1949 Cleveland Indians card:
See the split legend at the bottom? That was a feature of only the 1949 print run. That card shows the 1948 champs from a 1949 printing. I wish it was a 1948 because it would have Paige and Doby rookies.
If you actually look at the Phillies card:
It designates the team as 1950 NL champs. It is from the 1951 print run. Not 1950 because they wouldn't have known who was going to win the 1950 pennants until the season was over.
I know this is not what you want to hear, but the facts are what they are. Your refusal to recognize them just makes you look like you are cravenly trying to boost the value of the Mays cards you are hoarding.