I organise my groups in species.
For example:
A ~~~~~~~~~~~~~
A1 ~~~Dogs~~~
A2 ~~~2008~~~
A3 ~~~2009~~~
A4 ~~~2010~~~
A5 ~~~2011~~~
A6 ~~~2012~~~
B ~~~~~~~~~~~~~
B1 ~~~Cats~~~
etc
Its pretty easy to manage, plus its easy to see what you are missing. :)
For example:
A ~~~~~~~~~~~~~
A1 ~~~Dogs~~~
A2 ~~~2008~~~
A3 ~~~2009~~~
A4 ~~~2010~~~
A5 ~~~2011~~~
A6 ~~~2012~~~
B ~~~~~~~~~~~~~
B1 ~~~Cats~~~
etc
Its pretty easy to manage, plus its easy to see what you are missing. :)