Hello Steve,
In fact, according to J-Larcade, it was the AKO of 21 September 1915 that prescribed silver trim for dragoon helmets (except for the GDR1).
But for private soldiers, the AKO of 6 April 15 ordered the exchange of noble metals (brass and nickel silver) with grey-treated steel.
As a result, only Dragon officer's helmets were available in nickel silver.
In practice, under the helmet cover, I'm not sure that all Dragon officers replaced their old 'gold' helmet with a 'silver' one. Let's not forget that the officers were at the front, and that other more important things could take up their time (besides, Amazon didn't deliver to the trenches in those days).
Conclusion:
The Dragon officer's helmets of Brian, made in accordance with the AKO of 21 September 15, (silver version), are extremely rare. This one is even rarer, as it does not meet the criteria of the 0fficier 15 model (non-retractable tip, post-side for Chinstrap, etc.).