This work explored the significance of the drying history dependent effect on in situ crystallization in spray drying. Analysis was based on actual single droplet drying kinetics at different drying air temperatures. This paper reports the changes in droplet T-g, T - T-g, solubility, and supersaturation based on actual experimental data as drying progressed. The glass transition analysis suggests that a critical crystallization period might be significant for in situ crystallization in spray drying. This finding highlights the danger in using the final particle condition, delineated by the dyer outlet conditions, as a measure of partial crystallization in spray dried particles. Extended analysis using the nucleation-growth mechanism pointed to the same crystallization phenomenon analogous to the critical crystallization period concept.