There are a couple of hundred original cornetti from the renaissance and baroque period. Most of them are preserved in museums around the world and some of them are even in playing condition.
The starting point to make cornetti during the revival of the early music in the 20th century were these surviving instruments and a few original fingering charts. Nevertheless, during the research made to bring the cornetto back to life several modifications were introduced in order to fit the modern taste (particularly regarding fingerings). This modified modern cornetto has established itself as the „standard“ cornetto, to the point that many players don’t even know that their instrument is not a copy of a museum instrument anymore.
In order to see a full description of the modifications which were introduced and the reasons which lead to them please read this full length article regarding this topic.
There are several instrument collections around the world featuring noteworthy cornetti, maybe the most famous being the one at the Historical Museum in Vienna and the one at the Accademia Filarmonica in Verona. It is not a coincidence that most cornetti are allegedly based on instruments preserved in these collections.
There are a few rare exceptions, but most of the time we can see museum instruments only through a glass, but 3D printing technology allows us to make exact replicas of them for study, and why not, also use them in concert.
The picture above shows exact 3D-printed replicas of three instruments from the Vienna Collection: a mute cornetto in F, a mute cornettino in C and a soprano in G. All three instruments are tuned in a high pitch (470 Hz. or even higher according to the player‘s technique).
Museum instruments are a precious source to learn about the real renaissance and baroque technique that performers used, the fingerings and the tuning. Many times the discrepancies with the modern versions that we tend to use will be surprising, shocking or enlightening.
Modern reluctance to use exact replicas of museum instruments is based on the fact that the instruments are deteriorated or have changed their properties in time or that probably the best instruments didn‘t survive till our days. According to that we tend to use modern revised and corrected versions of the instruments we find in museums (quite often unknowingly, it is indeed very difficult to find exact replicas of museum instruments on the market). At any case, the only possible starting point for any research are the instruments which have survived and we shouldn‘t preclude that we can still learn a lot from them before we start making modifications. We might even discover that they are perfectly playable as they are.