Zippy,
I'm a bit surprised that you went for shelter in Hockley bus garage, because it was seriously damaged above ground on the night of 22-23 November. 19 buses were totally burned out, 4 were partly burned out, and 88 more were damaged.
On the other hand, there would have been cellars under the old ticket block where the original winding engine and gear for the cable tramway (1888-1911) would have been. Perhaps you went down there. Conditions were rough at that time. I spent one night at that time in the pedestrian tunnel under the railway between Grasmere Road and Ashwin Road, about 10 minutes walk away.
My gran lived close by, and I have most of her diaries, but unfortunately not her 1940 one. She kept a brief record of everything that happened, and I have most of them from 1941 until 1975, but that doesn't help on what happened in December 1940.
At that time I was only seven, but I did notice things and had a good memory.
While smaller towns lost much or most of the central area, Birmingham suffered more damage altogether, but it was spread over a greater area, and the authorities decided not to publicise it, as they did about the Coventry bombing.
Peter