DEF Age Question

My understanding is that, if properly stored, DEF can last up to two years from manufacture date. But I'm assuming that DEF in the tank will degrade a bit faster. What are the potential adverse effects of having DEF fluid that's a few years old in the tank? I'm wondering if I should periodically drain the tank and put fresh fluid in there.
Maybe I'm worrying unnecessarily....but the SCR system is complicated and repairs can be expensive. I want to do everything I can to ensure its longevity.
Thanks.





