So condo established in 1816 between Neth and Prussia.
Then Belgium splits off 1830, formalised 1839, leaving half of former
province of Luxemburg to the Netherlands. This Dutch rump is today's
independent Lux.
Dutch kinds ocntinue as Grand Dukes of Luxemburg, but the Grand Duchy
becomes more and more independent as 1800s progress.
German-Dutch, German-Belgina and German-Lux boundaries are maintained as
per 1816 treaty of Aachen.
1922 Belgium gets Eupen and Malmedy and Vennbahn railroad as compensation
for invasion from Germany.
Lux gets nothing. Dutch were neutral, so no changes there.
1940, Germany annexes back Lux, Eupen and Malmedy
1945 boundaryies returned to where they were prewar, except Neth and
Belgium both get to administer (not annex) some of the more
complex/interesting German areas adjacent to their boundaries. These are
pretty much all returned to Germany with only very minor modifications to
the sovereign boundaries in the 1950s. As Lux had mainly river boundaries
with Germany, there was little advantage to changing its boundary, so there
were no changes there.
It is somewhat surprising that this condominium was not changed to give Lux
total control over the river up to the eastern banks after ww1 or ww2. But
perhaps the regime worked well for Lux and Germany.

Brendan