This is venturing close to a request for legal advice, which we can't give. If you want to be really sure what is legally correct, consult a real lawyer.
The way that copyright statements are generally used is that the initial copyright statement indicates who owned the copyright at the time that a work was created, with a year of creation.
If the work is subsequently modified by the same copyright holder, then the list of years in the copyright statement can be extended to include the year of the modification.
If the work is modified by someone else (person, corporation, etc.) who can claim copyright on the modifications, then a new copyright line is added with the name of the copyright holder for the modifications and the year of change.
The basic principle is that you don't modify copyright statements, except to add additional years of modification to your copyright statement.
When forking a repository, you should leave the original copyrights intact and only add your copyright if and when you make changes to a file.
Thus, if you originally forked in 2010 and have not taken over new material from the original repository and only made a change in 2013, the copyright should look like:
@copyright 1999-2010 name of original programmer
@copyright 2013 your names
In most copyright licenses it is not a strict requirement, but it is usually appreciated if you explicitly state which project you forked from and to change references to the project name to the name of your fork in files you changed to avoid confusion with the original if the file is seen in isolation.