We have kept our HK octopus card from our last visit Jan/2015.

We were in a hurry last Jan/2017 and we were not able to do the refund of 50HK$ that time. Can we still use it this Aug/2017 Visit?
I was wondering because we are visiting again this Aug. 3, 2017, if it's still possible to use the Octopus Card. Please share your kind advise. thanks much