If its a brand new, unopened bottle and has already got deposits of crystals in the bottom, its not going to last long once its been opened, so I would regard this as a "use it fast and use it up" bottle, not to be trusted for long term storage.
When crystals form in the bottle, you have to realize that an important component of the developer is coming out of solution, and that means the characteristics of the developer are changing. There is a point at which sufficient material has dropped out of solution when the developer has changed enough to be very different in action than intended. The original Agfa Rodinal used to last forever, but R09 does not. In my experience, once opened, it lasts for less than a year under ideal conditions.