The tl;dr is:
If your receiver provided a copy of a message that was used to produce a multilaterated position for an aircraft then:
a) that one position will count in your site stats as a mlat position;
b) your piaware will receive all multilaterated positions for that aircraft for the next 3 minutes
For your receiver to be used, there are a lot of factors in play (e.g. happening to hear the right message, having synchronization with other receivers hearing the same message, rate limiting in the solver, local receiver density, etc), many of which are out of your control, which is why step (b) exists - so long as you manage to get one contribution every 3 minutes, you’ll get a continuous track.