Reading about all this in English is a bit confusing. “Possession d'état de Français” has a more specific meaning: It means being treated as a French citizen *by the French authorities*. Concretely, you need something like having been granted a passport, voting, or serving in the French army. As far as I can tell from your question, nobody in your family has done anything like that since 1914 and if that is indeed the case, the 50-year rule definitely applies.

Promoting French culture abroad, locating (or trying to locate) your family in France, feeling a strong bond to the country, being called “Frenchy” by your friends, etc. simply isn't relevant and *does not* establish the “apparent status of being French” as you call it. In practice, this type of reasoning won't impress the *Service de la nationalité des Français nés et établis hors de France* and if you would apply for a *certificat de nationalité*, you would almost certainly attract a refusal. You would then need to go to court, which is always uncertain and costly under the best of circumstances and seems pointless if even your attorney does not believe in your case. So unfortunately I share the conclusion that **you will not be able to make use of your French citizenship.**