When this was shown at the 1892 Royal Academy annual exhibition, a sketch of it was provided in the Academy Notes. That sketch shows the participants as shown in this image, not on the other sides as incorrectly shown by countless online images, including the Source. Perhaps whoever originally flipped the image is left handed and wanted that to be dominant hand of the non-featured participants.

This is a detail image (top and bottom more cropped than the sides). A fuller (perhaps complete) image of the painting appeared in an 1894 issue of an illustrated weekly newspaper. That image appears to have some writing at the bottom right, perhaps the artist's signature and date. The writing appears to be left to right. If that image was somehow accidentally flipped in the publication process, the writing would be right to left. Unfortunately that has been cropped from this image (perhaps deliberately to avoid detection that the image, that's all over the internet, was flipped horizontally). Another fuller image of it appeared in the 1895 issue of The Windsor Magazine, next to an article about the artist. But, the bottom is too dark to clearly see anything.