But on AT&T page last official update is BRB5, BRC1 not show, so they have to announce first BRC1 then the BRD* you sayThe upgrade path has gone BRA7 -> BRB5 -> BRC1
Samsung announced that the normal S7 variants are getting Oreo in mid-May, so I would think that it will be a CRE* build with one more security update (S2BRD*) coming out soon before the May Oreo release.
PD: Official AT&T page just put BRC1 as last firmware, we are closer