There is a story about Alexander Bell getting the patent on the phone because his competitor (Gray), who filed his patent on the same day, stopped for lunch on the way to the patent office.
Always amazing to me that there were two patents for the phone filed on the same day.
Maybe there was no other evidence that could be brought to bear in that case. So filing priority won out.
Actually, they weren't. Elisha Gray filed what was called a patent caveat. . . not a patent application. A caveat was an old document that one could file with the patent office indicating that one INTENDED to file a patent in the future for a specified invention. it included drawings and description, but without claims, or proof of patentability. It expired after one year. Caveats were discontinued in 1909. A caveat does not carry the same weight as a patent application. Some argued that Gray had filed a caveat a month prior to Bell's Patent application and that Bell had bribed the examiner $100 to see Gray's patent and had stolen a key design element, the liquid modulator. However, since Gray's caveat was filed several hours after Bell's patent was filed, that is simply not possible.
There were actually EIGHT phone patents or caveats filed within a two week period. Sometimes technology just becomes ripe. . . when all things start coming together in science.