I noticed this as soon as I held my first series two card in my hand.
In series two, the lettering for the player's name seems slightly different. The inside black lettering appears to be just a fraction thinner than what was used in series one.
It's almost impossible to get a good scan to show this. The reflection off the silver makes it tough to get a good scan.
Tyler Colvin is series one and Randy Wells is series two. Compare the E's and the L's. I think you can see that the inside part on a series two card is thinner than the series one card.....I think!
Check some cards yourself and me what you think. If it is different, the question is why? I think it has been a long time since there was a change to the cards from one series to another. 1968 is the year that comes to my mind. Any other years since then have a mid-season change?