I was thinking about this while I was on the road earlier today, and I bet the other few degrees of advance came from your injectors wearing in. As they wear, the pintle sits lower in the nozzle, which compresses the spring less, and with more mileage the springs loose tension, both these will decrease your pop pressure, which will result in the injector firing sooner, or more advanced. If you had checked the timing before adding the second pump I bet it would have been higher that where you set it previously and because it’s a slow process you don’t notice the timing slowly changing, until it was dramatized by the fuel pressure change.