Quick explanation time.
There are two type of techs: Common and Rare. Common Techs are most techs, such as Tyonian Mines and Roman Rigs. They're usually decent and with no absolute build limits. The ones with build limits are usually regional or national wonders, meaning you can only build one in a province or one in an empire.
The second type is Rare. A Rare Tech, as you can imagine, is rare! Whenever I generate a technology, there is a 1 in 20 chance that it is rare (which is about to make the fact there are three starting rares amusing). A rare technology has an absolute build limit: only one ever. Once the unit/building is built, no more can be built. If destroyed, the building/unit is lost forever.
The benefit of a rare technology, however, is that it can form the cornerstone of future common technologies.
With that said, we have two more rares.
Oceania: Oceanic Mechanized Infantry
California: Norton Industrial Works
I also improved the building/unit listing so that the whole thing is a bit more readable. Unfortunately, importing into GoogleDocs is hot trash because GoogleDocs is hot trash compared to Excel, meaning descriptions are usually cut short. Expect tweaking.