Looking on the internet, it appears this is at least the second set of cards issued in the series. The other set, also 20 cards, is sold out.
I don't know when they were issued but those cards are numbered 1-20. Here's the checklist for someone.
1 - Forbes Field / Pittsburgh Pirates
2 - Ebbets Field / Brooklyn Dodgers
3 - Shibe Park / Philadelphia Phillies/ Philadelphia Athletics
4 - Polo Grounds / New York Giants/ New York Mets
5 - Yankee Stadium / New York Yankees
6 - Tiger Stadium / Detroit Tigers
7 - Griffith Stadium / Washington Senators
8 - Comiskey Park / Chicago White Sox
9 - South End Grounds / Boston Braves
10 - Memorial Stadium / Baltimore Orioles
11 - Sportsman's Park / St. Louis Cardinals / St. Louis Browns
12 - Sick's Stadium / Seattle Pilots / Seattle Rainiers (Pacific Coast League)
13 - League Park / Cleveland Indians
14 - Astrodome / Houston Astros
15 - Shea Stadium / New York Mets
16 - Hilltop Park / New York Highlanders
17 - Crosley Field / Cincinnati Reds
18 - Maple Leaf Stadium / Toronto Maple Leafs (International League)
19 - Municipal Stadium / Kansas City Athletics / Kansas City Royals
20 - Braves Field / Boston Braves