Selling the samples is what counts, but it's only samples collected in the system to progress, sold in a rescue ship that count.
If you can find a wingmate, one smaller ship can cold orbit indefinitely, maintaining aggro on the interceptor, while other bigger ships can just fire limpets and manage the scouts and swarm (if in space). This doesn't work too great in alert systems, where meeting interceptors in a wing is a something of a pain, but in invasion systems and control systems where you can find a planet surface, just waiting for an interceptor to come to you, this works great. I managed to get 81 hydra samples in one go in my ship, and could have gone longer but I ran out of corrosive rack space and it started to melt through my ship. It turns out that hydras are the easiest with this method, as it has such a short rearm period that it doesn't move very far, giving the sampling ships a break from having to try to keep up. Cyclops and medusas are a little tougher, as keeping them at a low altitude means they move up and down too much for limpets to attach easily, and chasing them upwards as they rearm means they'll eventually reach an altitude where they just take off into space. Basilisks are the most annoying, because they will move more than 5km away when rearming if you aren't focused on keeping up, and reach "zoom away" altitude faster.
We tried this in Hyades Sector IM-L b8-5, and got 20 pips at once (and we aren't even done turning in samples from the evening)
