Passenger Trains > Stopping at Metrolink Stations

What determines when Amtrak will stop at Metrolink only stations? I've been on some Amtrak trains that make these stops.

http://www.metrolinktrains.com/schedules/

The Rail2Rail schedules at the bottom say which Metrolink and Amtrak trains stop at which stations on the Rail2Rail corridor.

Even Better... Buried deep in Metrolink's website an extremely computer-savvy person can dig up the complete Amtrak Pacific Surfliner Schedule complete with a color-coded showing of regular Metrolink stops.

NB: http://www.metrolinktrains.com/documents/news_updates/AmtrakPacSurflinerNB_102907.pdf

SB: http://www.metrolinktrains.com/documents/news_updates/AmtrakPacSurflinerSB_102907.pdf

This is barring service disruptions such as broken down trains, vehicle or pedestrian strikes, weather... Anything which results in an Amtrak train handling passengers for a scheduled Metrolink train which will not arrive, or will be significantly delayed.

OK. Thanks for the information!