Total A/C: X ... With Positions: Y (SKYVIEW)

What exactly is the distinction here? What qualifies as a ‘position’ for an a/c to be put into this category?

A recent ADS-B position message or multilateration position result.

So old messages don’t count toward A/C with positions? How old does the message have to be before the aircraft doesn’t count towards this category? And if it doesn’t have a position, how am I still able to track it? Thanks for the help.

A position in the last 60 seconds. The source code is the canonical place to look for this type of thing: dump1090/script.js at master · flightaware/dump1090 · GitHub

Aircraft with a non-ADS-B Mode S transponder send messages that you can receive, but they don’t include position information. The position can sometimes be multilaterated (think “GPS in reverse”) without ADS-B given enough receivers and suitable conditions, but this is not always possible.