The missing Fifth level is missing.
Level Five: The I will get to it some day level.
This is the car that we see in a garage with a sheet over it and boxes stacked on it. Or worse yet one out in the elements that are rusting and decaying away and the owner says it is not for sale as I will get to it someday.
Some at this level are found as barn finds soon enough to get to one of the other 4 levels but too many end up just rotting away to a point they are not even worth a parts car effort.
Kit cars are often found in this state as they are bough and started but never finished due to people not having the skills to fix it or the kit car mfg. going out of business.
There could also be a Sixth level of 90% done but never completed. I have friends that will get a car almost to the end but they never finish the project. Sometimes it is just a need for a few parts or a lack of detailing to the paint and other areas to ready them for show.
This is less about the level of restoration of the vehicle (whatever vehicle one is working upon), but more about the level of restoration that the person doing the build / restoration are looking at, doing (at that moment in time, which may change in the blink of any eye), or what they may be capable of doing (skills, or how 'deep the pockets'', or a combination of the either)..
I saw one of those cars that sold at auction north of six figures, claiming to be all original, numbers matching, blah blah blah. Three months prior I was at Fall Carlisle and saw the car up close and personal in the grand stand display area. For all the effort put into it, the body tag was affixed with Phillips head screws. Hmmm, I wonder if the buyer saw this befor plunking down over $110,000.
I agree with many other posters that there are more levels.
Certainly there is the "Hey, have you worked on that _________ lately?"
a) "No, ran out of money for awhile."
b) "No, can't find the parts I need/want."
c) "No, low on motivation right now."
d) "No, wife found me several other things that need done."
e) "Sure! Why, I spent several hours on it just last, last, oh, when was it? Let me think... oh yeah, in February 2020."
I've got one that any of those answers fit... 😋