Reproduced here is an entire letter from Carl Burger received July 27, 1998 by Lou Jerkich.
C&PA is what you have found--Cumberland & PA [Pennsylvania]. I am glad to see that a fair amount of people who have gotten 1831 have actually showed an interest in the history behind NE Rust Belt Railroading.
On the Company mix question, I wanted to balance the game playability with the number of players in the game. The mix that is in the rules provides several areas of competition between players. It is designed to have three major areas of development: Boston, New York City/Philadelphia, and the West (Cleveland/Buffalo/Pittsburgh). This allows, in a 5- or 6-player game, two players per area with enough Rail Companies that mergers happen without a great deal of squeezing. This also works well in a 3- or 4-player mix.
I wanted to induce rail building and routes (many lines) rather than one or two that the average 18xx game provides. I am aware that the order of companies that come into this game is not based on the historical order. The historical order is actually too hard to balance. One of the shortcomings is [that] the NYC [New York Central] is not as great a force in the game as I would like to see. But game mechanisms need to be balanced, and the general playability of all companies under a consistent set of rules with NO exceptions for any company or companies was what I was striving for.
I do not by any means discourage people from trying a different company mix at all. Try your own!
The train mix is developed to produce a train rush at the purchase of the first "5" train. "2" trains were in use historically for about one third of the history of Rust Belt Railroading. This is why they last so long!
I looked at the peak rolling stock periods of each company historically and tried to bring most companies into a rolling stock % of business (box [cars] vs. passenger [cars]). Some companies (Penn., NYC, C&O, B&O) had to be scaled back to fit the game objectives. Others (East Broad Top, C&PA, Shawmut, Rutland, Maine Central, BAR) needed more tokens so they could be playable. The Penn. had over half of all the total rolling stock on the Eastern States. Well, anyone who started a company that big would have no reason to merge. Any companies that merged could not get near the amount of capital equipment allotment the Penn. already had! Let's just say that I wanted a game that played well, too, and leave it at that!
Why each group?....To add just enough into each of the three regions to balance the game to the number of players.
Please note: There were several small roads I left out of the game because
they were too small or duplicated routes. (Note I included Lehigh &
New England [LNE] and left out two [companies] that did basically the same
thing.) I wanted a selection of rail lines large enough that they all may
not start, leaving it to the players to choose which ones actually do start
in any one game. This was to discourage the ABC strategies I have seen
people play in 18xx games:
A. Raise Company X.
B. Do exactly the same thing with Company X.
C. Win game because there is no good defense against B.
In most 18xx games, if you play them enough, this ABC thing happens. 1831 was specifically designed to not have an ABC methodology. My intention with 1831 was not to do the small twist on the same old, same old (1830, 1829 or 1835 styles). These are all good and have their own merit. I wanted a new style and that required [me] to design a game that did not go with the flow!
I hope this answers some of your questions.