Since I make a lot of keyboard reviews I will slip a card in whenever I reference something about a previous review. I'll also try to incorporate a comparison video when relevant. I also will put in a playlist card If it pertains to the video. For example if I am doing a gaming keyboard I might put a playlist about a PC game I have been covering because odds are, they are interested in that game.
Just don't over do it. I usually use two cards. I will add a few annotations at the end but they are mainly invisible ones for links during my ending scene.