Recently, I archived in pocket pages the five 2018 Seattle Mariners’ minor league card sets. I have team sets for each of Seattle’s minor league affiliates starting 1991-with the exception of the ’97 Memphis Chicks. In addition, I have many sets prior to ’91.
The cards tend to use contemporary designs but occasionally feature a toned down, retro look. Since I don’t collect cards from other teams, I’m not sure how many different companies print minor league cards. “Choice Marketing” and “Grandstand” are the two companies used by the Mariners’ affiliates. With the proliferation of card template software, some teams may produce their own.
Card backs have the usual stats, biographical information and pictures. Frequently, advertisements are included, as teams seek out sponsors to defray the cost of production. A pet peeve is the lack of sequential numbering. Many of the sets use uniform numbers instead.
Mixed amongst the players, coaches and managers are oddball cards. Trainers are almost always pictured, and mascots show up in many sets. Also, I’ve encountered owners, general managers, teachers-of-the-year, military personnel and others. Check lists are common, with a team picture or logo on the flip side.
Since players move up and down within the organization during the season, it is not unusual to get the same player on two or more teams.
The average price for a set is around $12. I order from STB Sports in Mount Vernon, WA. https://stbsports.com/ To save on postage, I have the cards sent all at once in August, even though some sets may have been released earlier in the season. Using STB saves having to order from individual teams, and they offer pre-season discounts.
I present this as a public service announcement, since I know all of you need new card collecting categories.
SABR's Baseball Cards Research Committee 
I’ve been buying MiLB sets for my kids from the teams they’ve gone to see. It’s a fun thing for them to collect that’s different than anything I do. I long ago made the decision that these were a step too far though I definitely see the appeal. Especially in the way you’re doing it where you get a snapshot of the entire organization each year.
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I’ve been lucky enough to attend the game the past few years when the Yankees AA affiliate, the Trenton Thunder, has given away the team set of cards. Of course, these usually have a small logo of whatever company (Verizon, for example) that helped foot the bill. I have yet to rip the plastic off the 2015 set, which amazingly, according to the checklist, includes Aaron Judge, Gary Sanchez, Luis Severino and Greg Bird (also Tyler Austin, Jordan Montgomery, Mason Williams, Jake Cave, Tyler Wade and a couple of others who’ve had cups of coffee). I’m not a Yankee fan but that seems like a better than average bunch at Double A on one team
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Oh sweet. Trenton’s my local as well but they never have the cards available before I head out of town for the summer. I’ve gotten the 2016 and 2017 sets for my son so far and I’ll pick u the 2018 at the shop next spring.
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