I guess it was discussed somewhere here before, but I have the opinion that it also really depends on cultural circumstances.
Speaking by my personal experiences: for example, in Latin countries, it is almost impossible to have a super formal waiver signed by the mayor or someone like that. At the same time, it is quite easy to obtain official answers by email. So, a clear “yes, you can use this data on OSM” by e-mail is not enough? I wouldn’t say so.
However, in Germany, bureaucracy is taken to another level. So the above behavior is not tolerated by a fellow German mapper, because they are used to receiving formal government letters by mail (not e-mail), and they expect the same level of waivers in OSM.
So, a “whiter-than-white” truly depends on who you are asking (and where they come from).
Edit: the waiver proposed by OSM lawyers clearly aims for big stuff. Hard to use on a normal level (let’s say, asking for a small, specific data, by a small company or a small city department).