Wesmip1, sure the original idea was as follows:

Saturdays (and big carnivals) only all 5 states.

Selection is the first horse (working up from bottomweight by TAB nos. i.e. 12 runners so work up from no 12, 11, 10 etc) that has a c, or d in its form (do not confuse with "D") that's it.

Some varitiations arose, because of confusion when an emergency gets a run, so say the bottomweight in a 16 horse field is a selection but the no. 17 (emergency) gets a run because of a scratching; and also qualifies, personally I then back both.

Also some back the first 2 to qualify (which usually takes care of the above anomaly).

Some only back the first qualifier with a "c". (watch it as can be different selections of course)

Some only back if the absolute bottomweight (highest TAB no.) is a qualifier.

Some back midweek as well.

Good luck!