Quoted from jcg9998:

As you have already stated, Bally tested most of there games in the field during this time period. That is the reason for the small runs on some of the games.

Quoted from el-comico:

Axel,a few of the rare ones one can only guess at the reasons...there is little known of Bulls Eye and no one has seen one

Quoted from el-comico:

Anyone hear of one called Monkey Bash?...around 1967 for Bally...never seen or what it looks like.

Quoted from drsfmd:

First, with regards to your coils... they were probably not wrapped at all originally. Take a look at photos on IPDB of Bally machines from that era-- there are a lot of naked coils in those machines!
Secondly, as already pointed out...

Bally used their distributors to get prototype games out into circulation for short term testing. If the game did well, it would be pressed into production. If a game didn't do well, it went to the scrap pile. Operators filled out a form (see below) for those machines to let Bally know how they were doing on location. Most of the games that didn't go into production make sense... one need only look at the playfield on Joker to see that there wasn't much going on there.
Bali-Hi -- same thing (incidentally, though the game is credited to Ted Zale, it's actually a slightly modified design based on a drawing that Harry Williams sent to Bally).
Double-Up is another one that's just dull. I have my suspicions that it's not actually a Zale design. I don't know who the likely suspect is, but it looks nothing at all like the other Zale designs.
Six Shooter... wide open playfield with nothing going on.

Bull's Eye is the white whale. There's a single photograph that appeared in Game Room magazine back in 1995-- and that looks like it was a copy of a photocopy. I'm not aware of any other photos of the machine. BUT, there is a schematic available for the game... so at least an engineering prototype must have existed. Jim Patla says that games that didn't do well in testing were literally cut up with a chop saw and put in the dumpster-- so any surviving examples of these low production number games must be rare indeed. I'd like to think that there's an undiscovered Bullseye sitting in a basement, forgotten, that will someday see the light of day again... but I also realize that's really unlikely.
Red Max is a particularly interesting one to me. It's got a decent layout and seems to check a lot of the right boxes to be a hit... yet it failed for some reason. Also curious is the fact that at least 9 examples of the game still exist (and in reality, that number is probably even higher). That's a pretty high survival rate for a game that didn't do well on location and never went into production.

This one never went into production. According to Jim Patla, it never even got as far as the art department. Each new project was assigned a project number, and there are a number of those that never even got as far as a name (existing only as "813" for example). A whitewood was created, and wired up without scoring or features, just to bat a ball around and get a feel for the game. Some stopped at that point... and Monkey Bash was apparently one of those.