Same vulcan plans dropping multiple times

I mean, ive seen it happen to others too but I thought dupes of the plans weren't supposed to drop. Got 3 vulcan left arm plans.

It's frustrating, the plan drops are already rare enough and to get a copy of a known plan that we can't even trade....... fml

Edit: to anyone who reads this with the same problem (thank you to the commenters)

The vulcan armor plans and the vulcan mod plans are in seperate loot pools. 10% chance for armor plans, 5% chance for mod plans. Once you get all the armor plans, you may start getting duplicate copies of those instead of a mod plan until you have all the plans for the mods, if that makes sense lol