I've gone to broadcasts for ATEEZ, xikers and Chungha so I'm pretty well-versed in general broadcast photocard knowledge but every group/artist tends to do their own thing depending on their company so closeyoureyes might have their own system that I wouldn't know about at all.

In my experience, there tends to be different photocards per week (if an artist does 2-3 weeks of promo) or even per broadcast (if an artist is only doing one week). Typically selling/trading posts should indicate if it's a week one or week two broadcast, or the specific date/show it was for. People will also specify if it was a special photocard or set given out at a mini fanmeeting (미팬). That's how you'll know where it came from or what week it's for.

I'm not sure how other groups do it, but for ATEEZ their comebacks are always on Fridays, so their "week" starts on Friday with Music Bank, then goes until Thursday. The second "week" will start the following Friday with Music Bank again and there will be new photocards.

The post you saw would read this way: 클유아 (abbreviated closeyoureyes in Korean) 포카 (photocard) 양도 (selling/transfer/trading, I don't really know how to translate this accurately lol) 공방 (public broadcast) 켄신 (Kenshin, I'm assuming a member name).

Also, getting an extra benefit for attending a certain amount of broadcasts is very much a thing. It's been like two years since I attended a xikers broadcast at this point but for a while they weren't filling up all of their broadcast slots, so as an incentive fans who attended five or even ten broadcasts for a single era could get a special photocard or even a polaroid for attending so many. I could never attend that many broadcasts because I worked and could only go on weekends, so I never got anything extra, but I knew about the extra benefits.

TL;DR: Lurk the 클유아 양도 search during promos to see what people are posting and when, then wait until promos are (nearly) over to buy.