When you say "problem", I'm not clear on whether you mean there's a bug in what you're trying to do (in which case you such clarify what your bug is), or whether you just want help solving the "problem" that you've presented.

However, I can make a suggestion which might help you in either case.  You are clearly using the same hash for multiple purposes.  While this is not in and of itself a bad thing, it is potentially confusing to the problem at hand, and might be causing difficulties when iterating through the keys of the hash.  So I would suggest that you use multiple hashes for your data, at least in the beginning, where one has contains keys like "13341_27276.01", and the other contains keys which are filenames.

Once you've iterated through the %csv_data hash, you can then merge them as a final step, if that best serves your purposes.