Is "wenn zugegeben werden mußte" an idiom with a somewhat other "Bedeutung" than the literal translation "If it had to be admitted" implies; i.e. does "wenn zugegeben werden mußte" actually imply an admission ((Zu)geständnis)?
2 Answers
No
An example:
Wenn zugegeben werden musste, dass Zeugen bestochen wurden, dann sind die Täter zu bestrafen.
If it had to be admitted that witnesses were bribed, then the perpetrators have to be punished.
The German phrase zugeben müssen is an idiom as the English phrase to have to admit is.
In most cases, you don't literally have to admit something. But you do nevertheless.
Ich muss zugeben, so schlecht ist das britische Essen gar nicht.
Oh my. Why did you admit that? You've sunk the whole food trope!
Still, there are cases where the meaning is literal:
Ich musste doch irgendwann zugeben, dass ich sie nicht heiraten will!
At some time, you had to admit that. The sooner the better.