From what I have read up now the unification was not done under article 29 but with a seperate contract that the elected parties from the DDR and the BRD signed to unite the parts of germany. I am not sure if this was against the article 29 but I can’t find any information if it was or wasn’t.
The contract didn’t include anything about voting about it.
So who are you accusing of doing the wrong thing: The government of the GDR or the FRG Government, because is it still illegal annexation if the country being annexed signs a legally binding contract that it will become part of germany without a plebiscite.
Maybe it went against the GG of the FDR but then it wouldn’t really be an illegal annexation but a different crime if it wasn’t against the laws of the GDR or our definitions of annexation might differ.