Greenshift Corporation (GERS)

[Dutch1]

This means that ICM could theoretically be issued a patent that improved on a Greenshift patent and then claim that Greenshift was infringing on ICM's improvement on it. It may sound like bad logic, but it is good legal theory.

Yes it could, if Greenshift was using a technology that wasn't covered with their own patent.

However, your reply was:

If ICM's patents were in dispute, wouldn't Greenshift's original lawsuit have mentioned it, and wouldn't ICM have filed its' own lawsuit, claiming that Greenshift was infringing on its' own patented technology?

To do so ICM should have been confident that their technology did improve the GERS technology in an unique way and GERS was using the improvement made by ICM without having it in Greenshift's original patent.
So I think you answered your own question "wouldn't ICM have filed its' own lawsuit, claiming that Greenshift was infringing on its' own patented technology?".