The return of the relieved (scooped) surround coincides with the introduction of the V63 (or so it seems). Like with most hardware changes, there was probably some older inventory to use up before a clean transition was made.
There is a photo of an early V63 in the Smith book and it has a straight ring on it. P 115. But on P 114 there is a 75 4001 with what looks like a scooped ring, anyone? I think this is another one of those things like Grover tuners, no clear cut off date.
Some Shadows have the scooped surrounds, others (including mine) have straight surrounds, so perhaps late '86 was the transition period for treble pickup rings, at least for the BT ones.
