i am not sure what "main code" is supposed to mean (i am no native speaker). but there is a reference implementation by intel and according to matthew garret most real-world implementations are only slightly changed.
It could be one of those bugs actually, as I don't think the manufacturers use the latest version of the reference code. Probably they use whatever version was available when the project was started or whatever version the programmers are comfortable with.
> TianoCore – Open Intel reference UEFI reference implementation, 7061 files, >100MB of code, 10% of size of Linux kernel. Bigger than Linux core kernel
From Garrets linuxconf.au talk, year ago. As it is reference implementation, it is pretty much untested in the wild. So you can expect those "slight changes" to be mostly bugfixes.
Punchline is that Intel DOES provide pretty much all code for UEFI. And it is still bad.
i am not sure what "main code" is supposed to mean (i am no native speaker). but there is a reference implementation by intel and according to matthew garret most real-world implementations are only slightly changed.