I made a choir of 7 'wind instruments' back in 2018, wind as in sounds like a gust of wind (a terrible pun, i know). They are very similar to the ones you have made but instead of changing the length of the bell end of the instrument I made mine so they can change the internal volume of the resonating chamber (much like the way you were adjusting the small wooden plugs on yours). Mine can change pitch by over an octave, but the pitch shifts are not completely obvious because the chaotic nature of the sound they make. I really like the way you walk through building your instruments and it makes me think about a different design where the windway can rotate direction allowing it to hit the voicing at different angles depending on the timbre the player wants. It would also be interesting to have a telescoping tube at the bell at the end instead of a fixed pipe so that the instrument can be tuned to any number of pitches.

I used the research of Roberto Velázquez Cabrera, who is likely the world expert on precolombian ceramic instruments. I highly recommend you take a look at some of his research and the fantastic guides he has made for building replicas of many of the more unusual precontact instruments he has researched. Many of the instruments he mentions have uniquely chaotic sound characteristics.

I call these kinds of vessel flutes turbulence flutes, because they are the primary wind instruments to make use of chaotic turbulence instead of the focus on reducing turbulence as much as possible the way that classical instruments tend to. The one unique feature that they have is that they cannot have any holes in the vessel other then the one they use to produce sound because the holes interfere with the violent turbulence produced in the chamber of the instrument. This means that in order to change pitch the instrument has to change in internal volume without any tone holes. I think there is a huge amount of innovation possible in the realm of turbulence flutes and I feel like they are one of the most under appreciated kinds of wind instruments. (vessel flutes in general are also under appreciated!)