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Apatosaurus: Follow up

While searching the web for a a site that would give
me the correct names for the different parts of a
sauropods vertebrae I came across DML posts from 2004
which had mentioned alot of the material that was in
my post making mine for the most part redundant (and
looking back at the Gilmore Monograph some of the
information I gave was incorrect). However, I still
have a couple questions.

Is the presence of an accessory lamina subdividing the
infrapostzygapophysial cavity a characteristic used to
distinguish _A. excelsus_ from _A. ajax_ as it does
_A. excelsus_ from _A. louisae_ (it's not present in
any of the three figured cervicals I've seen for _A.
ajax_ [1840])? It's also not seen in the figure of C8
of YPM 1980 but is present in C8 of CM 563), I'm
assuming it is present in the other cervicals however.

Also the significance of anterior projections on the
cervical ribs of _Apatosaurus_ specimens in
classifying them has been undermined. However, the
anterior projections seen on  _A. excelsus_ and _A.
ajax_ cervicals would offer a different muscle
attachment point than the ventral processes seen in
_A. louisae_ and some _A. ajax_ and _A. excelsus_
cervicals, unless anterior projections grow from these
ventral processes as the animal grows wouldn't _A.
louisae_ have a completely different muscle structure
than CM 563? Which would also mean that CM 563 and YPM
1980, even being of the same species (_A. excesus_)
had noticeable differences in cervical muscles?

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