Repair work painter "wet on dry"

whether it is permissible to make corrections in this way,

Everything is permissible… bad work, good work. ;)

As part of defect rectification, the line is simply supposed to be painted over by a painting company. I doubt whether the execution or defect rectification in this form is correct, as I am quite sure that a transition will be visible.

A professional works, whether as a layman or professional/painter, by feathering a new brushstroke on the dry surface. However, personally, I wouldn’t worry if a trained painter does it. He will know what he’s doing.

as I am quite sure that a transition will be visible.

Why should you as a layman be sure, when you apparently have no experience and want to come along with DIN standards and leaflets, although here it’s about skill, dexterity, and craftsmanship?

A picture would be very helpful if one is to assess the execution of a job here. My answer refers more to an area that slightly stands out from the skirting board, thus more of a surface. If it is directly above the skirting board, the latter will probably be removed if possible? If it is not possible and the brushstroke would have to be very narrow, you will hardly or just barely see anything anyway, because the shadow casting, angle, various surfaces of the skirting board and the wall above will deceive the light incidence.

Tip: offer the painter who is supposed to fix the defects a coffee instead of suspicion and a leaflet, then he will also put in the necessary effort. Because you probably won’t see him again, even if you are not satisfied later or already insist on the disproportion of having the whole wall painted.

Essentially, it is only a question of whether it is permissible to remedy the defect in this form, since it can be assumed that a mark will be visible.

In my opinion, the method of rectifying the defect is up to the craftsman (one could now also refer to recognized rules of technology and manufacturer processing instructions, but especially the former I consider initially somewhat exaggerated when it comes to painting ...). And if a mark is still visible afterward, the defect rectification has not worked and he has to try again ...

Above all, it also depends on the color used! Some can very well be painted over afterwards without any problems and invisibly ...

You won't see anything anymore. The painters are really good at something like that.