A lot of the earlier cards did NOT use the prefixes, they were just member numbers. The prefixes were added later on. There are some more recent cards that might have an extra zero in front of the normal prefix like 0157 instead of 157. The prefix numbers listed in the Slot Card Guide Appendix came from an official list provided by Harrah's some time ago.
If you're interested in saving different prefix numbers and need a checklist, I have one on my website (www.slotcardtrader.com/harrahs.htm) that shows all the cards I have. All you need to do is clear out my X's and you'd have a blank form.
If there's something else you have a question about just let me know or post something here and I'll try to help.