The past few years I've come across many research papers about this specific subject. If my memory serves me well, I've some notes about the ZZ in this regard. Unfortunately I haven't got access to my notes at the moment so I'll probably append to this topic in the near future. In the meanwhile you can always consult public repositories with research papers. For example, scholar.google.com. Maybe these sources give you some tidbits to answer your questions. See, https://scholar.google.nl/scholar?hl=nl&q=plant+retardation&lr=&oq=plant+retar for example. Enjoy.

Thank you, Oyster. I'll look forward to your summary -- if you have time and access to your notes. At a more basic level, a commenter in this forum -- back in 2010 -- said that some growers in Thailand and Indonesia use a plant retardant called Paclobutrazol, sold under the brand name Bonzi, to control and minimize plant shape. I then looked up the instructions for using Bonzi and conclude it is a chemical I would only attempt to use if I were growing my sansevierias outdoors or in a well ventilated greenhouse (neither of which I am doing). . . and dressed in a hazmat suit! I'll look for other ways to keep my small plants small, and I'll resign myself to the fact that they may eventually revert to normal size.

sanny 2016 I
bought one of those same plants almost entirely out of curiosity to see if they would
turn out to be a regular boncel. I did question the seller and they stated that
no these were mini and would not get the full size of a boncel/starfish.
They told me they also sold the regular sized boncel/starfish as well. I
don't trust what they told me since the only dwarf boncels I have seen for sale
have all been from Thailand and were much more expensive.

If it is just a
boncel that has been stunted that fine but what really made me wonder was when
I asked them isn’t this plant the same as the boncel they told me they had never
heard of the boncel (I guess they never googled Sansevieria starfish). I asked them to see
a picture of a full grown plant and they gave me the run around so I just gave up. You are probably right that they used something on this plant to keep it small.

Elliot is right, light has a lot to do with keeping a Boncel stubby. Also, you could keep your mini Boncel in a tiny pot, much the way you would keep a bonsai, and that will help keep it dwarf if it is truly a chemical dwarf.

Related but not, I saw on another site a Thai grower showed one of his thick-leaves Sans growing in a glass container with its roots suspended in a yellow liquid. It had a large yellow stripe down the leaf. Someone asked what he was using on the roots and the grower posted a picture of the chemical. The person said he hoped he has a flame retardant suit he uses when he's around his plants!

if this is how people are dwarfing and varigating plants, with awful chemicals, I think it's best to leave it alone.

BD and Vitorama, thank you both for the feedback about the mini "starfish" sansevieria. I am growing mine in a small bonsai pot, and we will see if mine and yours, BD, stay small. That yellow chemical treatment you describe, Vitorama, sounds so lethal! Is that how the grower got variegation (the yellow strip) in the plant? It shows just how hardy Sansevierias are to survive such extreme conditions!

By the way I may be wrong but I was under the impression that the regular-sized Boncel is itself the result of chemical treatment of cylindricas with growth retardants by growers in Thailand. If that is indeed the case, does each individual plant have to be treated to grow that way or do the Boncel characteristics thereafter persist with pups from leaf cuttings and regular pupping? (This sort of circles back to the original questions that I posed, and I'm just curious about it.)

The most I was able to ever learn about Thai and foreign growers using retardants I learn by just digging deep on the Internet, and to be honest, there wasn't a lot. No one addressed keeping plants small throughout their lives as in Bonsai. My original Boncel was quite small and now the parent plant (original) is relatively small. It has grown larger pups, and thinner pups too. They are all outside on my lanai in the same bright light and get the same care. The parent remains moderately small, but I have split off two larger pups to give to friends.

I agree with Vitorama's statement about the chemical use of any agent on the roots to maintain a miniature plant. I have learned to simply love the growth of what I thought were Cylindrica Boncel, even though they just now look like normal-size fan-like Cylindricas. They are magnificent by themselves. I have one that is huge. Leaves are about 10 and 12 inches long, very plump, very prolific, grows large pups, loves the light. There is nothing like a beautiful 12-inch fan-shaped plant to get attention from your neighbors!

Sanny, that bigger Boncel is amazing! Can't wait for mine to get that big...! Nice job!