I've got the science, exocraft and construction terminals but no blueprint for any others. I've done all that the scientist and technician have asked and have no tasks outstanding. I'm guessing this is a glitch but can't see a way to move on.
So I downloaded the NMS Save Editor intending to add the weapons terminal. It installed ok and I have the latest NET framework but I can't get it to work.
I Open Folder Saves and it automatically goes to DefaultUser, which I guess is where the saves are, However I can't do anything else, if I click on Open it just says GOG, no slots or anything. I feel I'm missing a step or something obvious but what?
Any help will be much appreciated.

I don't recall seeing anything directly relating to this issue but I have experienced some glitches with the tech terminals that may be related.

In my case, the Farmer failed to trigger several tasks that lead to some key (or at least useful) plant blueprints. Disassembling and then immediately reassembling the farmer terminal didn't help; they remained stuck at their last message and didn't initiate a dialog for the remaining plant blueprints.

So I disassembled that terminal, along with all the others since I was finished with all tasks they were presenting to me, and went on my way exploring the galaxy and doing the usual Traveler things. Die, evil sentinels, die!

Recently, though, I took a chance and recreated the Farmer terminal and to my surprise they gave me the tasks that finished up the plant blueprints. So, me happy!

tl;dr: Try disassembling the tech terminals that you've already finished and forget about them for a while (fuzzy number, I know). Do some normal exploration, game saves, restarts, etc. Then bring back the tech terminals one at a time, starting with the Overseer. That might reset a bit somewhere that triggers the additional tasking and brings up the Weapons terminal in the normal course of events.

Thanks for that sounds like a plan, I'll give it a go.