No, and Yes.
No, not all blue slips are the same. Each specifically states the required document, supportive evidence that petitioner has to submit or provide to HCMC for further review of the case.
Yes, it's already typed up and ready to issue by CO at the point of interview. Note, the CO didn't just see your case on the day of interview for the first time. He/she has studied or the Vietnamese staffer already studies your case prior to the interview date, then recommend for certain decision (Blue/Green/White or PINK). In my opinion, the interview is the tool to confirm the CO's gut check! If your case is a total "diarrhea", run loose, guess what you'll get? If it's a solid case

(no pund intended

) Just relax, it's will come out ok (again, no pund intended)
Good luck.
chuck and kim