Top: Na I D EW evolution for SN 2006X (left) and SN 2014G (right) before and after cuts (empty and filled black points, respectively) and stacked measurements of points after culls in intervals of 15 days requiring minimum two spectra (red points). Horizontal lines indicate the stacked EW and error from all spectra that passed the cuts. A Bayesian linear fit to the red points is shown with light red lines (1000 realizations) and a corresponding median with a dotted red line. The resulting slope is negative with 68.7 and 93.7% probability, respectively for both SNe. Bottom: cumulative deviation analysis above/below (upper/lower triangles) the stacked EW (corresponding to the zero horizontal line) and its associated errors (dashed lines). Significant points are shown in purple.