Hi Mike... I wish there was a map showing the junction of Vauxhall Road with Erskine Street in 1868 to go with Directory published then... to explain why it name's Erskine Street as Adelaide Street (next to the Adelaide Arms)! Methinks something's gone on at that junction that involved the loss of two property numbers, namely 73 and 74. In another photo of the junction I've come across, the side (garden) wall of the corner building (which I think is number 75) doesn't look like an original wall facing a street, while the low garden wall at the front shows signs of it being changed to form a curve at the (I think new) corner.
In addition to not being mentioned in the 1868 Directory, neither 73 nor 74 are included in the 1871 Census (and not mentioned as being empty), and they're missing, too, from the 1861 Census... so this is why I feel it's number 75 is on the opposite corner to the Adelaide Arms.
The other thing is, it's Henry Saunders who would have had the larger house (77) as he's an employer (of 59 people!) as well as the father of Benjamin (his manager?) next door at 76... who had only just got married and most likely to be live in the smaller of the two houses.
As you say, I'll probably never know for certain... and that's really why I was hoping to find an address for the conservative club... and that it was indeed 77!!!
Best wishes
Alan