As
@Ilela said, the blueprints for GB you've already built are still needed. Once a GB has been built it can be leveled up to 10 in the normal way of putting in forge points. After a GB reaches level 10 they can still be leveled up (up to 99 I believe), but every level after 10 requires you to use a full additional set of blueprints before forge points can be applied.
For the GB you have no intention of ever building, yes, they are just garbage to clutter up your inventory forever more.