You're close with respect to the C64 border trick.
On the C64, you could pull the border in the width / height of one character in order to support smooth scrolling (coupled with registers to set a 0-7 pixel start offset for the character matrix). This was done so that the borders wouldn't move in/out while scrolling.
By turning this option on/off precisely timed, the VIC graphics chip never found itself at the "correct" location to enable the borders, and so never did.
Opening the top/bottom borders was done very early because it didn't require much timing.
Opening the left/right borders with static sprites happened soon afterwards.
Opening the left/right borders with moving sprites was particularly nasty because the VIC "stole" extra bus cycles from the CPU for each sprite present on a given scan line, so if you wanted to move sprites in the Y position and open the borders, you needed to adjust your timing by the correct number of cycles for each scan line, often done by jumping into a sequence of NOP's. There were additional complications, but that's the basics.
I think DYSP (Different Y Sprite Positions) on C64 was first achieved in 1988.
On the C64, you could pull the border in the width / height of one character in order to support smooth scrolling (coupled with registers to set a 0-7 pixel start offset for the character matrix). This was done so that the borders wouldn't move in/out while scrolling.
By turning this option on/off precisely timed, the VIC graphics chip never found itself at the "correct" location to enable the borders, and so never did.
Opening the top/bottom borders was done very early because it didn't require much timing.
Opening the left/right borders with static sprites happened soon afterwards.
Opening the left/right borders with moving sprites was particularly nasty because the VIC "stole" extra bus cycles from the CPU for each sprite present on a given scan line, so if you wanted to move sprites in the Y position and open the borders, you needed to adjust your timing by the correct number of cycles for each scan line, often done by jumping into a sequence of NOP's. There were additional complications, but that's the basics.
I think DYSP (Different Y Sprite Positions) on C64 was first achieved in 1988.