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main thing i would worry about is if they are in your "iTunes" or "Music" folder as opposed to fcctemp or "Downloads". if they're there, then if you clear downloads (or it does this on its own after a while), iTunes will lose the file.
you dont store the actual files on iTunes, its simply a program to look at your .mp3 files in a super organized way. the files are sitting somewhere else (to find out where they are, right click a song and hit "show in explorer" or something like that, and thatll take you to the actual folders where the .mp3's are stored.
if these two song files are nowhere to be found (usually organized into files for each artist) then you might have to do them again (and remember, when you're downloading, make a point to save them where you can bring them into the folder they're supposed to be in).
source: ive been working itunes forever and probs can help with anything