Both of these are good questions. Awhile back I too wondered about how to accurately date scorecards, AND, wondered if people might score vintage scorecards to fetch more $, as scored cards seem to sell better. I literally would look at the ink texture/color, compare the ink to other legit scorecards I had, etc. Not always easy to do when shopping online however. Also, I play Strat-O-Matic Baseball (SOM) and I remember when I was a kid I used unscored scorecards that my Dad would get at the Giants games, games he went to but didn't score (back then they had a business mans special for SF Giants games on Mondays, his boss would urge his employees to go to. Wish my boss would do that! I was very jealous, still am!). Anyway, I would use those old scorecards to score some of my SOM Giants games. I have no idea where those scorecards are today. Lost in one of my many moves over the years I guess. This is certainly an outlier, but it gave me some pause when wondering how many other SOM players might have done what I did
Like Doug I use retrosheet. Baseball Reference has way too many ads for my taste. Retrosheet is all text, laid out simply, and you can go down rabbit holes looking at all the data on their website
Anyway, I wish I had started collecting scored scorecards years ago. They make great companion pieces!