It would be good to do something like this and go through every change to the .proto files since the last release to verify whether all new fields are marked as new in 1.4.0, if they are.
git clone https://github.com/p4lang/p4runtime
cd p4runtime
git diff v1.3.0 HEAD proto
For example, this PR appears not to have such comments on new fields that it added: https://github.com/p4lang/p4runtime/commit/fee499a02261f7380070e34d9edf4ab5c4ac59e5
It would be good to do something like this and go through every change to the .proto files since the last release to verify whether all new fields are marked as new in 1.4.0, if they are.