There is NO such TSB, period. Volvo has nothing in print on ATF change intervals but most people who see these cars daily have different opinions on that. Even VCNA people say that ATF should be changed on occasion.
Now...there IS a TSB (or TNN) about doing a trans flush using Volvos synthetic ATF in the event that the customer has minor shift related problems with the trans. The #1 thing that I've also experienced is that at about 60mph, the trans can do some wierd shifting or shuttering (like a vibration) and doing the flush with Volvos costly synthetic cures the problem.
If out of warranty, the stuff costs about $16 US per liter and the TSB says to use 16 liters to flush out all the old fluid, including the last 3 liters needed for the final fill. If it were my car and you prefered staying with the generic Dex III, then I'd flush mine every 20-30K miles depending on the fluids color and it turns dark from heat, not impurities. As mentioned in another thread here about adding an IPD filter, one guy suggests adding a good trans cooler instead and with an XC, that's probably a good idea too. You shouldn't have dark brown ATF in your trans because the stuff has broken down and isn't lubricating as best as it should be.