one of the most freeing (but equally maddening) aspects of force building is that most of the restrictions are self-imposed. You could take all from one list or the other if you wanted to. Don't forget about the Inner Sphere General list in addition to the house and provincial lists.
For the time in question (circa 3100):
- Where does the unit sit in the quartermaster's pecking order?
Units with more clout, eliteness, and political ties will get access to newer, shinier toys. Such a formation is more likely to get a fresh-off-the-line Carronade where a less favored unit has to settle for a refurbished Hercules. A unit way down the list might be lucky to get a 3049 vintage Orion ON-1M
- Does the unit engage in heavy combat with a specific enemy?
Let's say your theoretical unit is stationed close to the volatile border with the Lyrans. You'd be within your rights to add some salvaged mechs like a Razorback, Uziel, or Axman. A particularly experienced unit might even possess a clan mech or two either salvaged from the wolves or purchased from the sharks.
- When did the unit get its equipment?
A unit constituted or rebuilt after the Jihad is going to lean more toward provincial than national because that's what's more readily available coming out of factories. While different ex-members traded with each other before the reforming of the league, there aren't any guarantees. Also things like the Republic mothballing Irian's plant in 3091 happened.
On the other hand, a new unit down the priority list might get hand-me-downs or castoffs from other units so your rebuilt third battalion, third company might work just as well in 3060 as 3100.
