Q:

At what point do you drop attribution to original work?

Lets say I have a project which has evolved over the past year. When I began the project, I looked around for open source projects which provided as much of the base system as I could find, and finally settled on an Apache 2.0 Licensed project.
Over the past year, the project has evolved a lot, leaving very little resemblance to the original project. Basically the only similarities left are the project's source directory structure, and ideas left in-tact here and there (very few complete class files are original, most are either totally re-written or mostly due to this project's requirements).
At what point do I stop attributing to the original project? At what point have I diverged so severely as to be safe in saying I own copyright over this entire work as well as licensed under my terms?

A:

Never
As long as the project's code has a direct descendent to an Apache 2.0 License you should never remove attribution.
If you do a greenfield project where every single line is new and not copied over, then you can remove attribution.
There are some things you should never cut corners on, proper procedures around licensing are one of them.

