Wow! You must be quite the applicant, if one little request got you 25 sealed letters in record time!! 😀 You are going to need copies of whichever of those letters you decide to use to send to each school for which you complete a secondary. At least two of them, maybe 3, will have to be from science professors, and 1 from a non-science professor. I would say you should hand the sealed letters over to a letter service somewhere. However, the letter service might require that the letters be sent directly to them. If you don't have access to a letter service, then you may have to send the letters back and ask that your recommenders send copies to the medschools at the proper time, at which time you'll provide them with stamped, addressed envelopes for their convenience.
Talk about an embarrassment of riches!! But I wouldn't say that they'll be that useful for waitlist situations. In that situation you're trying to convince the school that the you and the school are a perfect fit and that you'll definitely go there if taken off the waitlist. These letters will probably be far too general and addressed to the quetion of what kind of doc you'd make rather than what kind of school would be the best fit for you. If the letter is one you're certain will be absolutely glowing, then you'd have used it at the beginning of the process. 7 or 8 letters is probably the most you'd want to send to any one school. Most schools are perfectly happy with 3 or 4. Tulane even specifically says not to send more than 3.
