Seems to come out a lot of new concepts these days. Topps crossover is cards that comes out but in digital and physical form and from different series, both sports and non-sports as I understand it. To this date there has been two sets, one for baseball and one for soccer.
http://www.topps.com/collectibles/trading-cards/topps-crossover.html
How should we deal with these in the database? Should each set released be a separate set in the database? Since they are released at different dates and in different sports and even non-sports probably.