GP and GPB zone formation in AI-Cu-Mg alloys proceeds rapidly at room temperature immediately subsequent to STQ. This structure evolution is well known for GP zones but not for GPB zones. In many age-hardenable Al-Cu-Mg alloys this vacancy assisted diffusion of Cu from solid solution to form zones is essentially complete within 50 hours with only a small residual quantity of Cu remaining in solid solution. The alloy then remains in this metastable state. This zone formation is observed here using Cu-63 NMR for the alloys AA2014 and AA2124 which lie in the alpha-theta (GP) and alpha-S (GPB) phase fields respectively. However these zones which form so readily at room temperature are unstable on aging at higher temperatures. Rapid dissolution of the zones, and their reversion back into solid solution at elevated temperatures is explicitly demonstrated by Cu-63 nuclear magnetic resonance (NMR). At this stage the Cu is shown to remain stably in solid solution at room temperature. Further aging at the same elevated temperature is then shown to reform the zones with further continuous evolution to either the theta-phases (AA2014) or S-phase (AA2124).