In 1924 Alexander Ross was granted a patent for "Improvements in or relating to Bag Pipes" which you can read more about here. Robertson not only produced this bagpipe for his long-time friend, but he also produced Great Highland Bagpipes for several years that followed the same profile. The pictures herein pretty much tell the story. Extreme angles, square cuts, wide, flat beads, and centered scribe lines on the ferrules. This was very different from the bagpipe that his father apparently made (bearing the shield dated 1914). The one thing that did remain more or less constant was the detail built into the projecting mounts.
This Robertson bagpipe shows some of the same features and profiles. The silver tuning slides are hallmarked 1925. Note the center-scribe lines on the ivory ferrules. 
Although both being flat-combed and with a similar profile, the bagpipe below has conventional scribe lines on the ferrules.
I have a feeling that this last Robertson bagpipe was nearing the end of his early profile. The angles aren't quite as severe, the beads not quite as flat, and the center scribe line has started to drift. His early bagpipe was in stark contrast to other Edinburgh bagpipes in style and in sound. He might have been influenced by what was happening elsewhere or James Martin might have had a hand in changing things.
The projecting mounts on Robertson bagpipes were always distinctive with sharp detail just below the bead. Mounts can be found made from white or black casein, wood, catalin, and, of course, African elephant ivory. There were several different profiles used and the size of the mounts changed over the years.
Robertson bagpipes in white casein are spectacular, in my opinion. The quality of casein used by Robertson was far superior to that which was used by Henderson and other makers. Other makers were quick to abandon the material in favor of catalin however Robertson produced bagpipes using casein into the 1960's.

You can find Robertson projecting mounts made in two pieces. They are threaded into place and reflect superior skill in manufacturing.

When I'm studying a bagpipe, I see the profile first and then look at specific details. The proportion of ring-to-wood-to bushing can be an important clue as to the maker and date of manufacture.
The miniature bagpipe to the left would have been made close to the time Robertson was making the Alexander Ross bagpipe.
Robertson - The early years