I guess Revit does it's thing to prioritize a correct volume instead of a "correct" length (I'm assuming this because length can be interpreted as Datum, while Volume and Area are "real elements")
As you can see in the image below, it only returns a "incorrect" number on the second wall, which makes up for the lost 18cm on the intersection with the 60cm wall:

If i extend the central wall, the calculation of lenght "jumps" the crossing one, and now we have 2 incorrect values:

But then again, they are only compensating for intersections and in this case. It only gives the same value because I'm not "slicing" either the 300cm or the 158cm wall. If I were to do that, the same difference would appear:

I would say that if you need a paper project, it's going to have dimensions on it or measure with a scalemeter. If you need a digital project, you can measure everything as needed. But if you absolutelly need to have every dimension absolutely perfect on a schedule, you should do as @barthbradley suggested and work a loooot.
Thanks for bringing it up, that was very clarifying for me, if someone ever asks for a schedule with every length, I'll take Revit's answer with a grain of salt.
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