The three removable build plates came from the same sheet of aluminum, albeit with different histories and somewhat different construction details, so they’re pretty much the same thickness. After leveling the sub-platform, I built three objects in one session with a single maximum Z height setting in start.gcode to see how things changed.
These measurements are from the Outline extrusion around the objects, with the number of data points (units of 0.01 mm) depending on the actual length of the side. Of course, I should have built three identical objects, but there’s only so much I’m willing to do for Science…
A 45 mm Companion Cube on Plate 1:
A pair of slightly tweaked nophead Polyhole test plates on Plate 2:
A completely failed 3D Knot (too large = too much overhang) with a very small Outline on Plate 3:
Things went quite literally downhill after the first object, but only by 0.2 mm. Unfortunately, a 0.50 mm first-layer height (when you expect 0.33 mm) is entirely enough to prevent adhesion to the ABS build surface and ruin at least the first few layers.
On the good side, the platform remains level within 0.05 mm, which is down around my measurement resolution.