If I remember right (2 days ago!) the front speakers were on the bigger harness, the backs on the smaller harness, so that could explain it. The smaller harness had a few other things like amp control I think - it wasn't just speakers but I don't think it was anything important.

I can probably get more detail from the instructions with the harness I got (later tonight when I get home), but I think that just showed wire colors and what they are for the aftermarket harness, which is now deep in my dash.

Worst case senario - spend $15 and get a new "95-up" nissan harness. If you are using the Pioneer without the amp now, it might be easier to start over since it will be different.
Or - someone must have posted more detail on the specific wiring pinouts sometime in the last 10 years! This is one of the few things that did not chance in the 05.