Western Germany recognized the border between Poland - the Oder-Neisse line in 1970.
There was no final settlement until 1990. Because you cannot give up claims on territory you don’t actually control, the ROC is in a similar situation with Mongolia. In Germany’s case there’s the additional complication that until 1990, occupation statutes still applied.
This implied there was only one Germany, in area and population greater than just Western Germany.
No, it didn’t. First off, the preamble isn’t actually part of the constitution, secondly, it did not in any way or form claim rule or sovereignty over the Eastern states. “We’d like to re-absorb those territories” is a different thing than “those territories remain ours”.
Also, German public broadcast used the upper left map for weather reporting up until the 70s, when they switched to the one on the top right without any borders.
Until the early 60s, both sides claimed to be the successor state to the German Empire, the GDR dropped that claim with the construction of the wall. After literally a decade of discussion the West changed to the Neue Ostpolitik in the early 70s and recognised the GDR as a separate state in its territory but did not change its own self-conception as successor state of the Empire. With that it also stopped applying the Hallstein doctrine, stopped to consider other states recognising the GDR as sovereign to be a hostile act.
Then came the two-state period, then there was a revolution in the GDR and while we call it reunification, legally it was the absorption of federal states which happen to be on the territory of the now-former GDR into the constitutional framework of the FRG. Nothing special, happened before with Saarland. If you want to draw a parallel to China I guess you can make one: To the until 1960 situation, with the PRC saying “There’s going to be trouble, ROC, if you move to any other position, it’s the status quo or proper unification no alternative”.
Also, German public broadcast
…is not controlled by the government, least of all the federal government which is responsible, or at least co-responsible, for all foreign policy (but religion and culture because there the federal states are completely sovereign). It does reflect the political attitude back then: That the status quo borders were “arbitrary” and until there’s a better set, the old ones still somehow apply even if it doesn’t match the situation on the ground. The switch in 1970 was the broadcasters throwing their hands up in the air.
And you know what I think the map until 1970 is missing the border to Denmark if I’m not mistaken.