finding changes on a branch

[Andy Howell]

I have a branch with subbranch:

1.66
 |
 +-> 1.66.2.1 - main branch
     ...
     1.66.2.9
           |
           +-> 1.66.2.9.2.1 ( Branch 1.66.2.9.2 ) - sub-branch
     1.66.2.10
     1.66.2.11

I need to apply the changes between 1.66.2.9 and 1.66.2.9.2.1 to 
1.66.2.11. If I use the revision number, I can get a diff:

cvs diff -r 1.66.2.9 -r 1.66.2.9.2.1 somefile.cpp

cvs stat on somefile.cpp says:

Sticky Tag:  patch1 (branch: 1.66.2.9.2)

If I try:

cvs diff -r patch1 somefile.cpp
or
cvs diff -r patch1 -r HEAD somefile.cpp

I don't get and changes.

I can't figure out how to specify the revsions using the branch tags. 
I'm trying to express "take all the changes on my patch1 branch, and 
apply them to the head of the main branch".

Thanks,

        Andy