Rosin gets dry after a while. I havn't tried myself a 10 yrs old rosin, but I have seen people using very very old rosin and they seem to produce enough sound. After applying your rosin, if your bow produces good sound, it means the rosin is ok. But for sure a new rosin and a good quality rosin plays a big role in sound quality. I hope this answers your question. Happy practicing!
RE: Rosin Tricks