That works until you see what appears to be 9 sprites on the same scan line in the border region.

Not quite. Drawing a full sprite-sized bitmap would not be so smooth on the C64.

They are in the border, Only sprites, ghostbyte (a repeating byte only shown in black. It is the last byte of the chosen videobank) and background color can be displayed there.

VIC II doesn't have that functionality. the first commodore that could do this was the Amiga series.