[split] Distances between files and ranks

[Renatus]

Is there any possibility in this passage that the two thousand veterans should be subtracted from the total number of 45,000, rather than being included in it or (perhaps) additional to it?

I don't think so. They were 'distributed throughout his whole force'. The word translated as 'force' is acie, which I understand to mean 'battle-line'. This is the term used in the Penguin translation. As Caesar has just described how Pompey had drawn up his forces for battle and said that they totalled 45,000, there seems little doubt that the veterans are included in that number.