Sorry, but there is not possible parallel. The possibility to reach 2400 rpm, and even 2590rpm, is clearly stated in the manual. We know how to rev up the engine, and there is not a single statement, in the manual, about the fact thath the throttle doesn't work once reached, say, 2200 rpm. So we have to assume that it works at least until 2590rpm.
On the contrary, there is one described system to overboost the engine, and is clearly stated that this system doesn't work over 2000m, and is clearly stated why it doesn't work. So, if there isn't the description of another system to overboost the engine, we have to assume that this isn't possible over 2000m, at least for the version of the engine described in the manual. There is not a "lack of text". There is a clear statement, followed by an explanation of how the device work and why it doesen't work over 2000m.
However, we can add something, due to pure physics. The possibility for the overboost to be obtained only up to 2000m is intended at takeoff rpm, so at 2140rpm. As well as the "quota di ristabilimento" (the maximum altitude at which the supercharger is able to provide 822 mm hg) is 4000m at 2250 rpm (potenza normale).
Given that the supercharger is directly geared to the cranckshaft, at higer rpm the supercharger rev more, and gave more pressure. So, the automatic barometric control has to mantain the intake valve more closed to mantain the 822 mm hg, so the overboost lever will work at an higher altitude than 2000m.
For the same reason, at higher regime than 2250 rpm, the supercharger can provide 822 mm hg at a higher altitude than 4000m.