I have purchased multiple plans from the Broker for mods, and they do not show for crafting at the workstation. I have received them through the mail, and used the item received, but they do not show in my plans listing.
If you have archived the exact same R&D plans on one character it will archive for all your characters on that account.
This is the only character I've grabbed plans on... I hadn't played in a while, and I believe the crafting system had changed. Still, I'll check. And thanks for the advice!