Fired ad glass panels take as much work and time to make as producing lenses.
Most people aren't going to go to the time and expense to make reproduction ad glass.
Especially when there are over a dozen different sizes that were used over time.
In the almost 20 years I've been making reproduction/fantasy globe lenses, I've only had 2 customers willing to go to that expense.
So IMHO any add glass panels you are likely find 'in the wild' are originals.
Later . . .