Have you taken account of the wind? If there is a 50 kts wind and an aircraft is flying into it, it's groundspeed will be reduced by 50 kts. On the other hand, flying the opposite way will add 50 kts. This means that two identical aircraft flying at the same airspeed will have groundspeeds 100 kts different. I suspect that the programme you are using indicates groundspeed.
I know it's a while since I retired but I doubt that any civil aircraft would file an airspeed of "620 mph" and aircraft don't fly fast to stop the one behind hitting it!!!!
I think you need to read a few books on aviation...