That's a tuff question to answer, Steve, but let me make a stab at it.
I would say there is a "classic" form for most "types", but then you have individual
factors that come into play such as the ability of the knapper and types of material
used that can cause alterations to the "classic" form. Different lithic material can go
hand in hand with different geographical areas and the use of local raw materials.
Charles C. Jones Jr. wrote in "Antiquities of the Southern Indians", 1873,
" It is hardly proper, however, to pursue this attempt at classification any further.
Were we to note all the varieties which suggest themselves, we would be led into a
multiplicity of illustrations which would do little more than represent the individual
skill and fancies of the respective workmen, the various casualties to which these
implements have been subjected during the process of manufacture and subsequent use,
and the modifications of form consequent thereupon."
Geographical names may represent a "core area" of distribution, but does not necessarily
mean that is where the first of that type was found. When Joffre Coe first used the name
"Guilford" it was for the whole Archaic and Paleo periods and all the different point types
therein. His name for the Woodland period and its' point types was "Badin". It wasn't until
after digging at Doerschuk, 1949, and discovering the sediment layered stratigraphy of
occupations, that a definition of point types was able to be attempted. And then came the
names like Morrow Mtn, Guilford, and Savannah River.
I like the above mentioned Projectile Point ID site for showing the "range" of different types,
but prefer Art Gumbus site for identification; http://www.lithicsnet.com/
And the Coe Foundation for Archaeological Research, ( CFAR ), has recently added an
Artfacts Identification area to their website; http://www.coe-foundation.org/
which is probably the best for the Southeastern US.
Sorry about ramblin'on but I hope this helps some.
Like I said, Steve, that's a tuff question to answer but there's two cents worth.
Joe