Eight histograms over raw observations, binned on ONE shared set of edges and counted on one shared scale, so the whole distribution's slide to the left (newer cohorts finish faster) is the picture, not an artifact of per-panel binning.
plotOptions.histogram.range and binWidth into
every panel: identical edges by construction, so the same bar always
means the same interval. The y scale is shared over the bin
counts (not the raw values, which live on a different axis
entirely). Binning each panel to its own extent would put different
intervals at the same x, which is the classic way a histogram grid lies.
Trellis is a premium feature; without a license it renders with a trial
watermark.