Difference in scoring between slrnpull and slrn with shared score file

I’ve got a shared score file for both slrnpull and slrn. I expect
that nothing below 0 points should be downloaded, and I run slrnpull
with the --kill-score 0 flag.

However, some messages still seem to "slip through" this filter,
and only get scored when I open them in slrn. For example, I might
see that there are 5 unread messages in a group, but after entering
the group (pressing enter), the counter resets. I’m assuming that
slrn is loading the score rules at that point.

My conclusion is that slrnpull has some kind of simplified scoring
mechanism, but I’d like to know exactly what the difference is between
the two in terms of scoring.

Any insights would be greatly appreciated.

My slrn and slrnpull versions are both 1.0.3.