Could you please tell me the name of some reliable supplements that meet those standards?

I have visited three private neurologist and they did not any kind of cognitive test to me ( by the way, they also did not let me explain the majority of my symptoms or the mechanichs of the accident, and I was not able to tell them because of my cognitive problems made me barely able to start a slurred sentence and unable to understand very well what other said. They also were incompetent and negligent enough to say that it's impossible to suffer from neurological problems without hitting the head and losing consciousness and cleared me to do fighting sport) .
What should I do to have this kind of tests done to me?

Read the Vitamins sticky at the top.

The neuros who claim no injury unless loss of consciousness are ignorant. There are plenty of head injuries where the head never contacted anything.

The mechanics of the accident are not very important. Symptoms are.

Is there a teaching hospital near you? They usually have a medical school next to the hospital.

A physiatrist (Physical Medicine and Rehabilitation) or neuro psychologist that is affiliated with a neurological rehabilitation hospital or clinic is usually a good start. Do you have any concussion clinics?

Many patients want to tell the doctor too much information with too much anxiety. This tends to cause doctors to back away. Plus, there is not much a neuro can do for a concussion.

Starting a good vitamin regimen seven months or more after the initial injury is too late, or can it be still beneficial?

As far as I know there arent' any

Any time you start a brain focused Vitamin regimen is good. You would be wise to get started and stay with it for life because your brain has been compromised. It will never heal completely so taking good care of your brain will improve your long term experience.

Have you seriously looked for concussion programs? I can't search foreign language services but most areas that have soccer/futbol, boxing/MMA, rugby and such have athlete based programs. Auto accidents cause enough concussion that neuro rehab hospitals usually have some experience.

-How can you be sure that it will never heal completely?
Aren't there many cases of people who fully recovered from similar problems ?

-Yeah, unfortunately I can assure that in the area in which I live there are not any.

Studies have shown that even though day to day symptoms may resolve completely, when the brain is put under stress, symptoms will manifest. The reason to maintain a brain health nutrition regimen is to increase the brain's tolerance for such stress.

One expert has even gone so far as to recommend that the medical record reflect any head trauma regardless of symptoms so that if symptoms manifest at a later date, doctors can have an understanding as to a likely cause.

According to those studies, how likely is for symptoms caused by a stress induced relapse to resolve once again?

Once the stressor is gone, the stress caused symptoms will resolve. For some, it make take a day or two.

This is one of the more common problems with PCS. The person feels like they have recovered fully then they go to a concert or other event with high levels of stimulation and need a day or two to recover. We just plan on needing time after to get back to normal.

It's been more than a week since I have stressed myself, and my relapse symptoms not only aren't over yet, but they are progressively getting worse each day.
It's that common? How likely I'm to recover?

You are still in recovery from your original injury. Your self-induced stress of nit picking every detail means you do not yet know what your long term recovery level is. You need to find a way to let go of your need to define every little thing. This obsession with every detail is very stressful and indicates you have more recovery to achieve.

As I have said before, Many do not see a good recovery until they either learn to let go of their obsessions with every detail or maybe get professional help and maybe medication to lower their anxiety and obsession levels.

You sound very driven. Your combative hobby also suggests a self-medicating to give you release from your intense look at life. Competitive people tend to struggle to let go of the details.

If you tore up your knee in combat, would you expect to be able to return to combat sports without a need to moderate your level of intensity?

Knees and shoulders rarely recover fully so athletes know to protect them. The brain is less able to heal so you need to protect it.

The studies show that those who learn to accept their brain as injured and work within its limits will do much better. Those who constantly fight every little setback will live a life of misery.