What time is it? Watches and horology

planning on making the decision on whether the caseback has been opened based on how much torque they need to use to open it themselves.

Sounds very dodgy to me. If it has been opened and tampered with it was sold to me like that!

Sounds quite unscientific. Are they fitted with a torque wrench in the factory? Probably not. And was it bought second-hand?

I assume you've asked your brother if it has ever been opened.