The criteria for mass shootings used to be 4 or more deaths but then it morphed into 4 or more injured.
The United States' Congressional Research Service acknowledges that there is not a broadly accepted definition, and defines a "public mass shooting" as one in which four or more people selected indiscriminately, not including the perpetrator, are killed, echoing the FBI definition of the term "mass murder"
I tend to use that definition but don't discern between whether the victim is killed or injured.
1. 4 or more people injured and/or killed
2. be in a public place
3. not related to another crime i.e. drug deal gone bad, armed robbery, gang activity
When you apply these criteria the number of mass shootings drops dramatically.
The subject is mass shootings, not mass killings.
If you apply the criteria you stated, specifically "1. 4 or more people injured and/or killed" then the number 307 as of Nov. 7th. is correct. It's now 309.
The Wednesday night massacre at the Borderline Bar and Grill, which left 13 people dead, including the gunman, became the nation's latest mass shooting, according to data from the Gun Violence Archive, a not-for-profit organization that provides online public access to information about gun-related violence.
In all, 328 people died in those incidents, and 1,251 were injured, according to the data. The numbers include incidents in which four or more people were shot or killed, not including the shooters, according to the archive.
https://www.gunviolencearchive.org/reports/mass-shooting