MIT accuses company of denying its researcher credit for anti-cancer device
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A similar thing happened between Atanasoff and the guys who designed ENIAC. It led to a huge court battle in the 70s where Honywell & CDC were fighting IBM and cie's patents. It was found out that John Mauchly, one of the two main creators of ENIAC, visited Atanasoff in Iowa while Atanasoff was building the first electronic digital computer (I'm sure that's debated) and learn enough about it that the court found that the patents he held with J. Presper Eckert were most likely lifted from research Atanasoff was doing.
The fact that those patents have been overturned today is good, else IBM would have killed the early PC industry.
Thus, a company can invest tens of thousands of dollars into a patent and millions of dollars into developing the patented technology and then an unnamed inventor may appear out of the blue and claim ownership.
So yes, it is important to name all the actual inventors.
BTW, this is not legals advice, just academic, theoretic discussion. There are many more complicated issues that can and will come up in real life, so I hope nobody actually tries to extract legal advice from this.