Here's the hypothetical situation ...
Our CEO (Joe) was coming to visit our office from out of town, and he wanted to see a report that we had been preparing for him. At the time of his visit, various organizations had been working on the preparation of the report for a month, and it still wasn't finished. I don't want to say who was working on the report, so I want to refer to the preparation using the passive voice.
So, could I say ...
At the time of Joe's visit, the report had been being prepared for a month
That sounds very strange, to me.
Obviously I could avoid the problem by saying
At the time of Joe's visit, the report had been under preparation for a month
but I'm interested to know if the first version, with the passive voice, is even correct English.