Peas, welcome to Sailnet. An introduction would be nice.
To answer your question: As you say, the proper oil filter for your engine is the Volvo 3840525. That is the one you should be using.
The other one is probably an aftermarket replacement for the original. An oil filter is hardly a sophisticated piece of kit, but, if it's time to replace it, I'd think you'd be crazy to use anything but the correct unit. Volvo engines are temperamental enough already..