The DOS Planets client (planets.exe), shareware Winplan, and their unpack tools have a limit of 50 scanned foreign ships each turn. Even if you see many more ships by means of an alliance, PHost will suppress the excess ships, and send them via util.dat. See also the relevant FAQ entry.
If you use third-party software only, you can use the bigtargets command to turn off this limitation. However, most current third-party software does not need that (VPA, EchoView and PCC can read ships from either place, other programs most likely can do that, too).
Registered Winplan users will always see all targets. When PHost detects a registered Winplan client, it will encode the "excess" targets in a format Winplan can read.
