Lanefan
Victoria Rules
Depends how one sees D&D development, I suppose.
For my own part I don't see it as being homogenous to era, as in all aspects of the setting are developed to a point matching X-century, no more no less. Some aspects or elements will have developed further and others (most notably gunpowder, explosives, and steam power) won't have developed as far, or at all.
I have it that in some areas marine technology and shipbuilding has got as far as galleons and clipper ships. In other areas they still use cogs or similar, other areas use biremes or triremes, while others use late-era junks or similar.
Meanwhile technology on land is also all over the place, historically speaking. Carriages and stagecoaches, for example, are at (at least) 19th-century levels of sophistication and design, road and bridge building is even further ahead (Dwarves are good for this!), and there's even some early - though still very rare - elements of powered flight coming online. Other aspects of society are nowhere near that point e.g. there's no paper money and most farming is still done through manual and animal labour.
Thus, having an 19th-century-style stagecoach roll up to the front of a still-in-active-use Parthenon in faux-Athens makes perfect sense to me.
Meanwhile in other parts of the world societies have developed in different directions, or in some cases are still at the hunter-gatherer level.
It's the Hercules-Xens mentality: take various historical eras, throw 'em in a blender, and see what comes out.
