Remember that Grizzly and most of the other import brands get their castings from the same sources, and the castings are used by different brands in different ways. The holes might be for a milling attachment for a completely different brand that happens to use that same bed casting, or that used it (say) 15 years ago when they first started making it.
Rick "never a fan of vertical milling attachments on lathes since inspecting one at Harbor Freight 20 years ago" Denney
Rick "never a fan of vertical milling attachments on lathes since inspecting one at Harbor Freight 20 years ago" Denney