A question came up recently about the practice of specifying the performing forces for a score using a string of numbers (e.g. 2-2-1-1, etc), and I expressed surprise that it bothered to also make a specific request for the numbers of strings (3-3-2-2-1, meaning three first violins, three seconds, two violas, two cellos, and one bass). An earlier question mentioned the much odder 2-1-2-1-1 (only one second violin, but two violas).
I'm not used to seeing string forces mentioned so explicitly—normally it's assumed that there is a section each for first, seconds, violas, cellos, and basses, and the exact numbers are up to the conductor to determine an appropriate balance, as well as the budget and availability. I assume that these pieces are not making unusual and highly specific requirements about the exact size of the ensemble, like Histoire du Soldat or the chamber-orchestra version of Appalachian Spring. I've seen this numeral code used in information sent out to players, but not on scores. But on the other hand, not being a conductor, I don't spend a lot of time looking at scores. Is this a more common practice than I thought? Is it, perhaps, meant only to indicate the minimum number on each part (i.e. "2-1-2-1-1" means that first violins and violas have 2-way divisi so you must have at least two of each, but of course could also have two seconds and two cellos if you wanted? Is this practice, perhaps, more common in materials aimed at school orchestras?