The hardware eras (at least the ones I listed earlier in this thread) pertain more to the Constance, Kelly, and (later) the Birkin models*. For other models, I believe much of the hardware in the 20th century was outsourced, so it may not have followed the exact same “rules”. Perhaps your bag is an example of this?
In a similar vein, it’s not impossible that Hermès made gold plated brass available for other bags earlier than they made it available for the Constance, Kelly, and Birkin. Though, this being said, I’m still quite surprised this brass is lacquered/plated— that wasn’t the norm which makes this all the more interesting. I’d be interested to hear what the artisan says!
*It applies to a couple of evening bags available in the 20th century too.