Ok, shuffle is off

I download a number of podcasts to a usb stick to listen to on the commute to work, however the car stereo (Sony) always plays them in reverse order of broadcast, as in the most recent first

eg

110 Episode 110_ No Such Thing As A.mp3

then

109 Episode 109_ No Such Thing As A.mp3

This isn't a massive pain although i would prefer them to be in file order eg 109, 110, 111 etc

How do i find out exactly what metric my car stereo uses to sort by, as i have found dozens of solutions but no clear answer to how exactly a Sony car stereo decides on the play order.

Yes its a minor irritation, but I just want it to work the way i want it to