It doesn't really change much in the glass bottles if they are still sealed. They stay pretty much the same as the day they were bottled until opened. So a bottle from March is the same as a bottle from August. The only real changes are in the settling and possible un-blending of the
juice through being kept still for a length of time. I have this picture of an example.
Left bottle is GCD in the old LDPE bottles before glass from about 9/14. Right is GCD from the glass bottles from 12/14 decanted into the old plastic that I reuse for decanting on 6/15. Big difference!!