The MOT test is not a comprehensive test of a vehicle. It is a mere compliance test to indicate whether a car is safe on public roads, for the general public. It was designed partially with the driver, but also other motorists, in mind.
However - I have long held onto the theory that an MOT test can tell you much more about a car's history.
Let me tell you why.
Oil Leaks#
ICE cars have lots of oil, and not just in the engine. Between the gearbox, differential, power steering system and several suspension components, it can be hard for even the most experienced mechanic to find the source of a leak.
A disaster scenario is for an oil leak presenting on an MOT to be coming from the engine. This is rare, but has been known to happen.
Even if it is fixed, it can reoccur. BMW made the genius move to use purely plastic oil pans. Combine this with a, usually, metal drain plug and washer and you have a recipe for disaster after a hasty or overzealous oil change. This started in the early 2000s, and has been getting worse since.
A more common scenario would be for a leaking shock absorber, or whatever equivalent exists on the whacky French suspensions within Citroen models.
Keep in mind that on most cars, the steering rack is conatined not far from these suspension components, hence why I say it can be difficult to tell what's leaking.
Overall, an oil leak on an MOT is not usually a big worry if it's been fixed. But if it reoccurs, you really have to ask yourself - how was this person driving?
Suspension Issues#
Not only can your suspension spray oil all over your underbody and give your car a nice advisory, but it is a wear item.
And though I mentioned in the Oil Leaks section that having a lubricated undercarriage can be a sign of bad driving, a more notable sign of this would be uneven or untimely wear on suspension components such as bushes or ball joints.
Not to mention corrosion (exposure to salt), damaged (not worn) shock absorbers (those damned speed bumps) and straight-up bent arms.
None of that should happen to a normal road user in England. This car has been ragged, and ragged hard.
I've long hated buying a used car and discovering an interior rattle within my first week of ownership. My completely untested, unproveable and unfalsifiable hypothesis on this subject is that you can simply crack plastics in the interior given bad conditions of roads. If you want a car that has been driven around like Alan Sugar's S class, my advice would be to those with past suspension issues.
Structural Corrosion, Rust#
Everything rots, everything changes. It's the inevitable cycle of all objects, animate and not. But you can speed it up within yourself, by smoking, drinking and generally being a nuisance to your internal organs.
Cars feel this too. Not the smoking, but when you spray their delicate metal with wet salt that disolves on icy roads and gets flicked all over your underbody. Of course, the alternative would be to not spread salt on roads in the winter - greatly increasing risk to life and property.
That being said - a car with a small delicate chassis, like an MX5, starting with an "S" (for Scotland, blanketed by snow for many months out of the year), can signal that it's on it's way out. Even if it had some welding and a retest, you'd be remiss to stock one of these, especially of an older generation.
Conclusion#
There are many facts you can infer from an MOT history, even from resolved items - but you have to be careful about what you try to infer.
The human mind looks for patterns, even when there are none. It tries to find explanations when it lacks the evidence.
I am currently doing research in the MOT history space - correlating government data with proven reliability records to find out exactly what patterns we can infer, and how we can keep the public safe from purchasing cars with a dodgy history.