I could not find an answer to this.

As an example, if I dont have blacksmithing and I buy a crafted blacksmithing armor piece, can it not be upgraded from that point?

I ask this because the upgrade patterns are BoP, whereas the crafted items are BoE. Can you use the upgrades (i.e Truesteel Essence) via trade window similar to how enchants work through trade window?

If not then it would seem its pointless buying crafted items that are not fully upgraded.