There is no definitive number of “stars” when it comes to Major League Baseball cards, as there is no official designation or criteria for determining stardom on baseball cards. Here are some insights into star players who tend to be highly featured and sought after on MLB cards over the years:

Throughout the early decades of baseball card production from the late 1880s through the 1950s, the sport’s biggest stars tended to be the most prominently featured players on cards. This included legends like Babe Ruth, Ty Cobb, Honus Wagner, and Joe DiMaggio. As individual players became true national icons of the game, they stood out compared to others in terms of the number of cards released featuring them in various seasons, sets, and card manufacturers.

Ruth in particular was one of the first true “card stars,” with his popularity in the 1920s driving strong sales of his cards and numerous variations released each year by companies hoping to cash in on his fame. Ruth’s iconic status and broad appeal to fans helped cement individual players as true stars and drivers of interest in the card hobby.

Into the modern licensed baseball card era from the late 1950s onward, two major forces have determined the number of stars featured prominently on cards in any given year or set – performance on the field and popularity/notoriety. Players who achieve statistical milestones, awards, or help lead their teams to championships undoubtedly gain more consumer andmanufacturer focus when it comes to card releases. At the same time, those with vibrant personalities or off-field fame that capture the public’s attention also tend to have more cards in circulation.

Some indicators that a player has reached “star status” in terms of baseball card popularity and production include:

Consistently being featured prominently in the base set rosters of the major card companies like Topps, Bowman, etc. Especially those released as the primary photographer card.

Having autographed, memorabilia, rare parallel or short-print cards produced with higher frequency than other players.

Appearing across multiple card brands/licenses beyond just the major manufacturers. Indicative of their name holding strong secondary market value.

Remaining in strong demand years after retiring, with their rookie and career highlight cards retaining/appreciating value faster than most.

Recognition by non-sports entities or reaching a level of mass market fame/notoriety alongside their on-field play.

Based on these typical markers, in any given season of MLB there are usually between 30-50 players at any moment that could reasonably be considered true “stars” or superstar level talents based on baseball card popularity, production levels, and secondary market reactions.

Some examples of consistent modern stars through the 1990s-2010s who routinely topped these categories include Ken Griffey Jr, Barry Bonds, Cal Ripken Jr, Derek Jeter, Chipper Jones, Pedro Martinez, Roger Clemens, Alex Rodriguez, Albert Pujols, Mike Trout. In the current era, names like Bryce Harper, Mookie Betts, Fernando Tatis Jr. appear to be on a star trajectory as rookies based on early card popularity.

Performance and fame are evolving targets. A hot, award-winning season can thrust someone unexpected into the top star conversations temporarily. Injuries or controversies can undermine a previous star’s card production. Rosters also expand in the modern game, giving more fringe players cards despite more modest playing careers.

So in the end, while figures evolve constantly, a reasonable estimate of the number of true “stars” represented robustly through baseball cards in any single MLB season since the late 1950s would fall somewhere between 30-50 individual players. With the number fluctuating annually based on that season’s top performers and fan favorites driving demand from the expansive community of card collectors.