I had to RENAME all my selection of Photos into a sequential "SEQUENCE".
What I had, which is most probably true for a typical photographer/videographer, was a selection of Photos that I'd taken and/or edited OUT of a continuation of SHOOTING.
I have looked through the Vegas Help Files and read and re-read Forum input on this and I could not unearth this. It would be a "good" thing for a warning to be programmed that would flag out-of-sequence photos/images and should Vegas proceed?
As a longtime User, I don't regard this is as User Expectation. I didn't!
I do hope that SCS take on-board my feedback and make changes to accommodate my suggestions above.
Grazie