(Please refer to entry of February 23, A Mysterious Picture.)
I have made a return visit to the La Madeleine in Preston Center. I have still not penetrated the women's restroom but I did take a picture of the picture in question. Some answers have been revealed but new mysteries arise.
The third chair is clearly placed at the second table. Therefore, whoever has been drinking the cup of coffee is left-handed. The red wine, however, turns out not to exist. What I thought was wine is in fact the refracted image of the window sill in the woman's glass. So they are not sitting drinking wine, they are pretending to drink from empty glasses, possibly a charade for the benefit of the men at the street corner.
I planned to take the picture down and see what information was on the back, but it is surprisingly heavy. I felt the backside of the picture and it is papered over, so there would probably not have been any information in any case.
The women's room remains out of my reach. Not only are the toilets just off the kitchen doorway, they are also in full view of the table staff uses for its breaks.