Hi Joanna,
So when we had +1/+2 CR before these changes we endeavoured to ensure that these were done by different people and if a maintainer gave a +1 they resisted also giving a +2 as we recognise having multiple eyes is always advantageous. So the general feeling was that this should be the recommended best practice. However, the feeling was also that this specific recommendation should not be strictly enforced by gerrit checking as on occasions it is possible to give both on simple patches and maintainers and code owners in this case can be trusted to make the correct choice.
Like I mentioned, I think both options are perfectly reasonable here. I also agree that it doesn't seem necessary to be particularly strict about the enforcement for now. As you said these should be general guidelines and it may be useful if maintainers can overrule them in specific situations.