past perfect continuous passive

Because there is no past perfect continuous passive in the English Grammar Profile, we can say it is C2.

A search in NOW corpus shows that this grammar is extremely rare.

1   HAD BEEN BEING TREATED 10

The woman had left the Ulster Hospital, Dundonald, where she had been being treated.

belfastlive.co.uk

2   HAD BEEN BEING ABUSED 7
3   ‘D BEEN BEING ABUSED 7
4   HAD BEEN BEING USED 7
5   HAD BEEN BEING TAKEN 4