What is the effect of improper joinder on patent validity?
According to MPEP 805, improper joinder of inventions does not affect the validity of a patent. This is based on the last sentence of 35 U.S.C. 121, which states:
“the validity of a patent shall not be questioned for failure of the Director to require the application to be restricted to one invention.”
In simpler terms, this means that even if multiple inventions are improperly joined in a single patent, this alone cannot be used as grounds to invalidate the patent.
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