Zach of RPGBlog2 writes about the Rolemaster:Rome supplement. In it he wishes there was more on the geography and the city of Rome while there was great stuff on Roman life. I am not sure what issues the author of Rolemaster:Rome faced in his research. I know from my own attempts that trying to create a historical setting can be frustrating with the materials at hand. Even with the power of the internet somethings are just not readily accessible. Others are filtered through a author's point of view and omit details that would have been useful for a campaign.
But despite this, most DMs who want to run a historical campaign can overcome this by using their knowledge of the period to make stuff up that fits. The point after all is to make something gamable and fun and not be the final word in realism.
To illustrate this lets take S John Ross' Medieval Demographics. Part of the heart of Ross' article is a series of professions with SV values. You divide the population of your target settlement by the SV the result is the number of that type of establishment or professional. Any result less than one can be used as a percentage that will exist.
Very simple, very elegant, plus has the benefit of feeling right to those up on medieval history. However where did it come from?
If we look among Ross' footnotes we find that this section was developed mostly from a table found in the Life in a Medieval City by Joseph and Frances Gies. A book I happened to have.
On Page 236 we find this and see where he got his starting point.
This table is based on a 1292 Paris Tax Roll. By now you notice that the SV value is not the same as what in the table. I think what S John Ross did was divided the numbers above into 55000 and did some rounding.
Notice that the table cuts off at 21 why? Because it turns out the authors omitted any profession that had under 21 professionals.
Putting my Google-fu to work it turns out that this particular document has been transcribed to the internet.
Occupational By-Names in the 1292 Tax Roll of Paris.
As you can see there is a lot more to this list. Most of the distinctions are too fine to be fun or particularly gamable. Do we really want our players to care whether they need to go to an bow & arrow maker or just the bow maker. Most DMs don't. You can now see why there are so many darn Shoe makers in Medieval Demographics. Turns out 1292 Paris had a lot of Cordovan leather shoe makers. 222 guys and 4 ladies. Heck time travelling roleplayers would be set. There are 8 dice makers to choose from.
Hope this illustrates some of the issues of creating historical settings. If you are going to do so there is going to be some editorial choices that you will need to make.
P.S If I figured out S John Ross' math right those dice makers have a SV value of 7,000. (rounded of course).