When did the NEW patents expire?

Everyone says Gillette went to Trac II due to competition in the early seventies from third party DE blade Mfg's like Wilkinson and Personna but I know Personna and Star and others were making modern style DE blades as far back as the late 40's.

Gillette hatched the NEW in order to have exclusive blades since anyone could mfg the old 3 hole blades. How long after the introduction did the NEW blade patents wear out and every company in the world start making blades to fit the Gillette products??
Thanks
Wp

In 1931, Gillette merged with Probak in order to avoid litagation over the design of the razor blades. I am not sure when the patent on the shape was up, but the goodwill razor is a great example of how the razor and blades went through a series of contorted shapes to keep brand loyalty. By the time the 50's and the 60's rolled around, I think the major issue was thin and stainless. The actual shape patents must have been long gone by then.