Our integration project was going well until we actually integrated with other parties. Our tests passed, their tests passed, but integration failed.
After inspecting both implementations I noticed a difference in version of the messages assembly. (0.4.0.0 vs 188.8.131.52)
In NServiceBus V3.0 and onwards subscriptions for types with the same Major version are considered compliant. This means that a subscription for MyEvent 1.1.0 will be considered valid for MyEvent 1.X.Y as well.
After using the same mayor version for the messages assembly we could finally integrate.