I found this about KLM flights and the use of Global Upgrade Certificates. Not the same thing, for sure, but it might follow the same rules.
Redemption on KLM – ROYAL DUTCH AIRLINES
- Valid on Delta-marketed, KLM-operated flights for use globally on published Main Cabin fares booked in Y, B, M, H, Q, K, L, U, T, X or V class to Business Class.
- Valid on all KLM-marketed, KLM-operated flights from published Main Cabin fares in Y, B, or M class to Business Class.