Variants of a mold are catalogued separately, so each one has its own sets and minifigs. Check these too if something you expect is missing here.

• 18937c01 Vehicle Base 8 x 16 with Wheel Arches, Front and Side Studs, and 4 x 14 Recessed Studded Section, 3 Holes, Dark Bluish Gray Wheel Clip Pins this part is a alternate of it
• 18937c02 Vehicle Base 8 x 16 with Wheel Arches, Front and Side Studs, and 4 x 14 Recessed Studded Section, 3 Holes, White Wheel Clip Pins Alternate of this part