As Mr P has said, a full range of iron bench planes make their first appearance in the 1938 Marples catalogue - if you look back ten years to the 1928 issue, the only metal planes then were a couple of iron block planes.
The 1930s was not a good time to innovate in toolmaking. The second world war meant that many Sheffield manufacturers switched to armament production, and even for those still making tools, steel would soon have been in short supply. So, as a generalisation, tool making slowed down or stopped for the duration.
After the war, it took a long time for production to pick up again, what with war damage and the loss of many skilled workers. So by the time things were 'back to normal' much of the market for hand tools had disappeared, ready for small electric motors to become widely available and change everything again.
That's one reason why Marples planes are relatively rare, though they did at least continue to make them. I have a 1960 Woodworker magazine which features a supplement listing all the planes generally available then, with prices, and Marples are there alongside Stanley, Record and Woden. Marples bench planes were the M3, M4, M4½, X4, M5, M5½, M6 and M7 with several of them also available with a corrugated sole. (Of course, the pictures are not in colour, so there is no help there.)
Another factor to bear in mind is that almost everything branded as Marples could also be had branded as Sorby - same tools, same price. (A bit like Bosch/Siemens/Neff for white goods.)
I don't know of any published studies that will help you, but it's very likely that there will be relevant information in the Hawley Collection - catalogues, accounts and mint samples of tools in their original boxes. It's a huge resource with a handful of dedicated volunteers looking after it. I'm sure they would be welcome you if you wanted to make a study - but you'd have to go to Sheffield to do it.