^This one is the toughest painting of the bunch for me to pin down. There's just too much going on from possible different sources. The jet-shaped head in the robot and alt mode is like a late-'70s super-robot or even an early '80s live-action Super Sentai robot. The huge shoulders are definitely late-'80s anime style, while the legs sort of look like something out of Mospeada
(3rd Gen Robotech), as seen below...
But there's not really any "smoking gun" I can find with that painting that's a single obvious design source.
So when all is said and done, I'm afraid I can't state for sure the origin and purpose of those robot paintings.
However, I will offer a couple final opinions about what those paintings are NOT...
They are NOT unused Takara designs for the Transformers line.
1. Assuming the Takara dates stamped on the back are legit, Takara would not have been custom-designing robots for Hasbro's TF line in March of 1985. There were still plenty of pre-existing Diaclone and MicroChange designs being used that year.
2. The alt modes in the paintings are all futuristic, non-realistic looking vehicles. In early 1985, the Transformers vehicle modes were still mostly based on normal earth machines (not counting the Dinobots and Insecticons of course). TF: The movie
was still far enough away that there would have been no demand for Cybertronian or futuristic alt modes at that point.
3. The alt vehicle modes in the paintings also have a definite 1970s aesthetic to them that doesn't fit in with the 1980s-style Takara Transformers designs. The heads of the robots shaped like entire jet planes is the type of thing seen on gigantic 150 foot-tall super-robots, not 30 foot-tall Transformers. Plus, a couple of the alt-modes look too simplistic to be Transformer designs, particularly the "Daimos" truck (more on that one later).
4. Finally, the particular elements of a couple of those paintings that seem swiped from 1970s robots would have already been seen in the US in 1985, in the form of Bandai's Godaikin
line, which had been on US toy shelves since 1983.
They are NOT designs for Takara robot toys that were going to be released in Japan in 1985.
1. My main argument centers on this particular painting:
That basic robot form and particularly the vehicle form are totally recognizable as Daimos...
Daimos truck design and anime scene
There's simply no way that Takara could get away with a licensed design that looked so much like a well-known and unique vehicle from a pre-existing series. Not only in Japan is that true, but also in the US, where Daimos had been imported by Bandai/Popy as both a Shogun Warrior in 1979 and a Godaikin in 1983. Americans would have been fooled by the minor design changes of course, but not the Japanese. I don't think Bandai would have let Takara use such a similar design in either country.
2. The "mixing and matching" in those paintings that would fool Americans would not fool the Japanese. I could see a smaller, unknown company borrowing designs like that, or certainly a Chinese company, but not Takara. Aside from the likelyhood of being busted for it, there were plenty of original robot concepts around in 1985 Japan so that swiping designs wasn't even necessary.
So, taking all that into account, I have to say that I'm inclined to stick with my original position on those paintings. I think they are clever, fan-made (or unauthorized bootleg) designs stamped with a bogus Takara copyright just to excite discussion among American Transformers fans. They weren't produced in 1985, based on the designs used, so I'd say someone whipped them up during the 1990s or later.
That's my Japanese robot-geek's opinion, anyway.