I don't think it would've mattered in your case, going from LHR-BER.
The AC partner lounge network seems to be designed as AA departure lounges, the terms require same-day departure on an AA operated flight. They would not help for a partner-operated flight even if it is a codeshare. There are exceptions for other paid lounge programs, i.e. Qantas and Alaska, when you are traveling on that partner's metal