Alright, so I actually got quite intrigued with my little investigation into "best fullscreen", when it comes to the actual removal code. Since neither TNT Crew nor Omega stabilized their scanlines - who did?
Swedish New Year demo 1 (89-01-01) includes the "TV snow" screen by TCB (left/right/top), already mentioned in this thread. I can only assume TCB knowing Omega already having beaten them to the first true full screen didn't care to remove the lower border as well .. or maybe not, see later
On with the code. Short-form synclock btw.
Code: Select all
$00dda0 : 43f9 00ff 8260 lea $ff8260,a1
$00ddb8 : 7602 moveq #2,d3
$00ddba : 7800 moveq #0,d4
$00de32 : 41f9 00ff 820a lea $ff820a,a0
...
$00de3c : 4e71 nop
$00de3e : 1283 move.b d3,(a1)
$00de40 : 1284 move.b d4,(a1)
$00de42 : 720c moveq #$c,d1
$00de44 : 4e71 nop
$00de46 : 51c9 fffc dbra d1,$de44
$00de4a : 4e71 nop
$00de4c : 4bfa 044e lea $e29c(pc),a5
$00de50 : 7a00 moveq #0,d5
$00de52 : 1a1c move.b (a4)+,d5
$00de54 : e74d lsl.w #3,d5
$00de56 : 2c35 5000 move.l (a5,d5.w),d6
$00de5a : 3a35 5004 move.w 4(a5,d5.w),d5
$00de5e : 4bf8 8800 lea $ffff8800.w,a5
$00de62 : 0dcd 0000 movep.l d6,0(a5)
$00de66 : 0b8d 0000 movep.w d5,0(a5)
$00de6a : 4e71 nop
$00de6c : 4e71 nop
$00de6e : 4e71 nop
$00de70 : 1084 move.b d4,(a0)
$00de72 : 1083 move.b d3,(a0)
$00de74 : 4e71 nop
$00de76 : 4e71 nop
$00de78 : 4e71 nop
$00de7a : 4e71 nop
$00de7c : 4e71 nop
$00de7e : 4e71 nop
$00de80 : 4e71 nop
$00de82 : 4e71 nop
$00de84 : 4e71 nop
$00de86 : 4e71 nop
$00de88 : 4e71 nop
$00de8a : 4e71 nop
$00de8c : 4e71 nop
$00de8e : 1283 move.b d3,(a1)
$00de90 : 4e71 nop
$00de92 : 1284 move.b d4,(a1)
$00de94 : 4e71 nop
$00de96 : 4e71 nop
$00de98 : 4e71 nop
$00de9a : 4e71 nop
$00de9c : 4e71 nop
$00de9e : 4e71 nop
$00dea0 : 4e71 nop
$00dea2 : 4e71 nop
$00dea4 : 4e71 nop
$00dea6 : 51c8 ff94 dbra d0,$de3c
Now who would've guessed - it's stabilized

Well, TCB were already members in the Union then and I can only speculate that it was set in stone to have Level 16's fullscreen in the Union demo - released just six days after SNYD1 - which could explain both from where the original code came and why TCB didn't make their screen a fullscreen in SNYD1.
edit: I quickly analyzed the Union Demo as well. Main menu borders are credited to TNT Crew, and there seems to be no difference between them, TCB above and Level 16. I didn't count the exact cycles though, only some relative distances and that they were all of the dx,(ay) style.