Did you find the plots at City Road. They may not have a stone on them.The BB12978 plot I would suspect does NOT have a stone as you said there are other folks in the grave that are not connected.
Have you contacted Bereavement Services at City Road for help?
I can confirm that there isn't a headstone at the plot 12978 BB
There is a Headstone at the plot 14831 NN
I can send you a copy of the photo I have if you can contact my E-mail address (for some reason your email address wont load in my browser when I click the link below)
That Charles Robinson was my 3x great grandfather, although she doesnt appear on the Burials entry here his second wife Hannah was buried there but is catalogued as in AA 12798, a plot which does not exist.
Although Tony says there is no stone when I was searching for graves over 10 years ago I came across a stone inscribed with Charles' name along with some others. Sadly I didnt photograph it and havent seen it since, but I do remember roughly where it was ( I only went back a couple of times) . William Henry and some of his family are buried in AA 11168 and I walked all down that row and the ones immediately near to it. So good luck if you are going to have a search. Did you want to know anything about Charles?