Binding, how many services? Options

[6thDragon]

This came up during a run the other weekend. On page 180 is says: " binding is used to compel long-term service from a spirit the magician has already summoned." it goes on to say... "The magician requires one net hit to bind the spirit. Additional net hits beyond the first add to the number of services the spirit owes." My question is this: When you bind a spirit do the services from summoning them transfer? If you summon a spirit and gain 4 services, then turn around and bind the same spirit and achieve two net hits. What would be the final outcome? Would the initial 4 services expire at sunset or would you have a bound spirit with 6 services? If this is the case I wonder when it would be better to rebind a spirit as opposed to summoning a new one and starting over because it is much easier to gain services from a summoning test than it is from a binding test.