Hmm... looks like you're right... there would need to be some kind of "obsolete tech" tag to prevent it from showing up in your build options...
I thought for a while that the number under the upgrade option did the trick, but it didn't..
Adding a new tag is SDK, would anyone possibly be willing to do that for me please?

On another note, I added a canoe/exploration ship and started a archipelago game. It has been quit interesting, though I didn't really get to use the War Galleon era much. It was on normal speed though.
But as I have it most later ships need either the small or large shipyard to build, I need to make it higher priority for the AI to build the shipyards.
All I have seen for the AI is cogs, Galleass, a couple Corvettes (Which in fact need the small shipyard) and a trireme or two. All but the corvette do not need a shipyard.
What do you all think of a National shipyard like this.
350
Requires 5 small Shipyards, and 2 Large shipyards (Both which only allow you to build most ships, no extra XP or building speed).
Give 7 xp to new ships (as they cannot atm upgrade mostly, this will help get them a little more elite.)
%75

building of ships.
Comes with the Tech Steel.
Might need to be toned down, but as they cannot really upgrade now (Save SotL/Frigates to Ironclad Frigates and a few merchant types to another) it would help some.
Thoughts?