Adding Couple's mission onto their membership record

We have a couple that have served multiple missions and would like to have them listed on their record. Can you add multiple missions or just the first mission

I could be wrong, but I think it's just there for YSA being called on missions. Once they've served, they are not called again. The leaders need to know that to know who to encourage and who has already gone. I don't know as it applies to a couple mission since they can be sent out again.