Reserved IP numbers

["Holp, John Mr." <holpj@nwc.navy.mil>]

I am getting mixed results from different sources about the subject of
reserved internet addresses for internal subnets.

Most indicate that 10.x.x.x is for the category A network

and 192.168.0.0 though 192.168.255.255 for the C category

But the confusion is in the B category.

Some sources indicate it is;

127.16.x.x through 127.31.x.x

while others indicate it is;

172.16.x.x Through 172.31.x.x

It looks like a transposition error between 127 versus 172

127.0.0.1 is what I use for the loop back test and normally 127 is reserved
and not to be used for normal addressing.  I don't think of the 127 range as
being in either A or B category, rather a special case.  

Now 172 is clearly between 128 and 191 so this would point to 172 as the
correct answer?

So the question is which is correct?

Thanks 

John