Usually, there is a sticker on the computer box or timing belt cover. But sometimes they fall off because they are applied over dirt and oil.

If you bought the car locally, call the local Volvo dealers and see if it was ever serviced there. They will ask for the last 6 digits of the VIN.

1999 was the 1st year of the 105K belt interval change. Most owners had the belt changed at around 80K, not knowing better.

In your case, wear on the belt might be seen. Cracks show up on older belts.
In any case, if the belt was changed at 80K, the new one would be good for 185K max, along with a new tensioner. It is highly unlikely that the belt and tensioner are original to the car, most tensioners built in 1999 would have failed before now.

Klaus
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Volvoless. Sold the R. There is now a void...