There have been changes in bracing and placement, "forward shifted" versus not forward shifted, etc over the years, and so this description of the difference is only mostly correct
So, Martin introduces the D28 in the 1930s. It has certain characteristics and herringbone purfling around the top of the guitar. WWII breaks out and the herringbone goes away because that part came from Germany, and around the same time they switch from scalloped bracing to straight bracing. In the 1970s, a market has developed for pre-war Martins and so Martin figures out how to make a pre-war spec 28 and also realize that the bracing shifted towards ths soundhole in this period. So they introduce the HD-28, which has scalloped and forward shifted bracing, as well as the herringbone detail on the top of the guitar, meant to have the more open and dynamic sound of pre-war Martins. People also still love the tight and powerful sound of the 1950s Martins and so the D-28 remains on the market.
The D41 came out in the late 60s. I'm not sure the exact timeline of that model, but generally speaking (and for sure true of bogey's as well as mine from 2001) it is highly similar to an HD-28 with different cosmetic appointments and with wood pulled from a higher graded stack. Scalloped bracing, forward shifted, spruce (for sure sitka, not sure when they switched from east coast appalachia adirondack to pacific northwest sitka) top, east indian rosewood back and sides. Abalone on the top, fretboard, headstock, and string pins. Cool looking pattern inlay on the back strip. The D45 in comparison has abalone on the back and sides as well as the top, and is pretty identifiable by the abalone outlining the part of the fretboard that sits on the body. The wood is graded visually, I don't know exactly what characteristics they look for in the spruce to be rated more highly. Curious what the ebony is like these days on standard d/hd28s vs d41s, wouldn't surprise me if the 40 series Martins get the jet black and the 28s have a bit of white on them.