It was a subset, the players had regular cards in the set as well. In player checklists and team checklists, it will help differentiate the Captain card from the base card (and in Steve Yzerman's case, the All-Star card, too).
If we're going to put LL and AS (etc.) on stuff, we should be doing this as well.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).