Every aircraft is sending its ADS-B information on the same frequency – imagine you are at a party in a big room and everyone is talking at the same time. You may be able to hear and understand quite a few people around you. Someone standing just a few feet from you may not be able to hear and understand that same set of people; they may be able to hear and understand a different set, yet both of you are in the same room with the same conversations going on.
This happens with ADS-B, a lot of planes talking at about the same time, and your ADS-B receiver hears and understands a certain subset of those planes. Another ADS-B receiver in the area may hear and understand a different subset.
And there are many issues, starting with how many planes are talking, how far away they are, then moving to your ADS-B receiver an the antenna you are using, the sensitivity and selectivity of the receiver, and more.
It depends if those aircraft are transmitting positional information, or not
If you are running your receiver on a raspberry Pi - and look at the web page that comes out of DUMP1090. The table on the right shows planes in green - these are transmitting where they are and are the ones shown on the map. The ones in white don’t say where they are - just what height they are and can’t be plotted so simply.
The way the ones in white are plotted is by several people with receivers working together and form the signal delays calculating where the plane is - this is called multilateration or MLAT for short.