Top: after correcting the spectral index for extinction, many of the older Class I YSOs start to overlap with the Class II YSOs. These objects were higher in Figure 1 but moved down among the T Tauri stars in this figure. Bottom: plotting age (based on G. A. Feiden 2016 models) vs. extinction-corrected spectral index. A few stars have low gravity and are expected to be ∼1 Myr despite being optically visible Class III YSOs. Many other Class II YSOs are optically visible despite being less than 1 Myr old. We do not estimate ages beyond the limit of the G. A. Feiden (2016) models, or for stars hotter than 5000 K where the isochrones are very close to each other.