How can this be fixed in vic20 specific code when the viceo-viewport.c forcefully centers the picture to the border, when the VIC-20 itself does not do so?
that code is for centering the entire image within the viewport - ie the "borders" is the black area around the actual emulator picture when you eg go to fullscreen mode and dont have hardware scaling enabled. try switching to "full borders" in the c64 emulator - then the picture is not centered either..... but the vic20 code can not do that apparently.
the "debug" numbers are the actual limits (including overscan) - these are probably the only ones that are correct (because you can pretty much calculate them)
the other numbers.... i dont know where they come from. some of them i have interpolated from the others when i added the different border modes....
if you really want to dig into this, look at what the C64 code does for "full border" and port that to the respective vic20 code
and no, there never was a specific maintainer for NTSC - TLR did most of the recent vic20 stuff for that matter.
there already exists a ticket for it too: https://sourceforge.net/p/vice-emu/bugs/689/