But not 100% ? 
Check the schematic, datasheet and documentation.
https://www.arduino.cc/en/Guide/NANOEvery#features
There is a dedicated serial port to the SAMD chip which is used for serial-usb.
The Serial1 port a pin 0 and 1 is available.
I understand your point, and thank you for your contribution.
It is good that the SoftwareSerial exists, but it has many more disadvantages.