What is the name of your state (only U.S. law)? Colorado
A company is infringing on my patent and they say they were already showing and selling the product before my patent was issued. I filed the patent Feb of 95, they started selling the product in 96 and my patent was issued Nov. 97. How would the court rule in this case? Would it go by the filing date of my patent or the date it was issued? I also have several witnesses that know I was building my first product in late 94 if that would help.
Filing date. Once a patent is issued, everything goes back to the filing date of the patent (or the priority date if the patent claims priority to an earlier application or patent).
That said, the real
important date is the date the invention was "invented." The U.S. has a "first to invent" system, so the day the invention was conceived and reduced to practive is really the important date. The presumption is that an invention is "invented" on the filing date (or priority date) of the patent -- however, that presumption can be overcome by evidence showing an earlier invention date.
Also, as to "how a court would rule," there are really two issues here -- infringement and invalidity. Whether or not the other product is infringing is one question -- and that has nothing to do with whether or not they started selling their product before your patent issued. If they are infringing on the patent now, they are infringing. There is no "innocent infringer" or "independent development" defense for patent infringment in the U.S.
Damages for infringement, however, generally only start from the date that the patent actually issues, so if they had a product on the market before
your patent issued, then they would not generally be liable for damages on sales that occured prior to the issue date of the patent. There are exceptions, however. And generally, damages only start to accumulate in any event from the date you inform them that you think they are infringing.
The other issue is the validity of the patent. They may be challenging the idea that you were the first inventor. This is a separate issue from infringment.
So, the answer to "how a court would rule" would depend on (a) can you prove that they are infringing, and (b) can they prove that you weren't the first person to invent your patented invention, and therefore invalidate the patent.