Globally Challenged
Different fluid limitations?
This is probably it. And not different fluids necessarily. System design and maintenance procedures have to start with some number. And then certify the design/procedures. So it could be as simple as the same fluid with different limits set for moisture absorption.
You could go to the manufacturer and request recertification to new limits. But every system will have to be investigated (fuel, lubrication, etc.) at the new numbers. That won't be cheap.