it doesn't have to be @0, mostly it won't be
there is this freedom left in definition of CD medium
i wouldn't reallly know why
i guess maybe data synchronization, when mastering, the way they did it
was rather complicated process back then
so this would allow to overcome certain technological difficultties

generally CDs for older systems, like SCD, will have those offsets more random at wider range
most extreme values currently in DB must be around several thousands

So, I assume, the additional offset would be a factory offset or mastering error?

That puts Mad Dog McCree at -298. Which seems WAY off.

That game has to be the worst mastering job ever. The exe date in the header and the exe date reported by the actual file are a year apart. Same date, different year. Which I can only attribute to human error.

those listed @AccurateRip are drive offsets
they are indeed constant

value px_d8 returns is combined offset (drive+CD)
you'd use this value for EAC offset correction
knowing drive offset, you can derive CD offset
CD offsets are required for DB

so you must run px_d8 with each CD

from your example, assuming drive offset is +30
you'd rip Ground Zero Texas with offset correction +30 and submit 0 to DB;
Mickey Mania with +32 and submit +2

it would be better at first to compare some CDs to already existing DB entries
if there are none, maybe audio tracks of Mickey Mania are comparable to European release

I am preparing to archive my collection of every USA Sega CD release and obviously am looking to do it in the most accurate way possible. I even purchased a new Plextor Plexwriter Premium for this purpose.

After going through Rocknroms stickied MegaCD/Saturn guide I'm left with an issue...

Ground Zero Texas: I run the px_d8 tool and come back with a combined offset of +30. A number that matches the AccurateRip offset DB.

Mickey Mania: I run the px_d8 tool and it reports a combined offset of +32.

What's the issue here? Should I be running the px_d8 tool with each new disc I rip? Seems to me that the offset should be something that's constant.

I really don't want to continue without really nailing down a process for what I'm doing.