I don't know what book your reading, but I just opened up my 97 PCM file, (should be the same as his also)it lists both a P0171 and P0174 both with SES enable.
The only thing the computer needs to do is pull fueling from either bank or any piston it wants to. When it doesn't see a change or does see a change (even in just 1 O2 sensor) it determines which bank it is based on simple algorithms. Its like the 3 light bulbs in a room with no windows and the light switches are on the outside of the room. You have to figure out which switch goes to which light without leaving the switches on.
1997 Pontiac Bonneville SEi-SCRAPYARD
2000 Chevrolet Blazer LT 4X4 4.3L
2002 Chevrolet *-10 LS Ext Cab 4X4 5.7 V8