Recovering "Damaged" Files on External USB Drive: GUID, HFS (can not open files)

I had some files on an old thumb-drive, and recently I was going through and discovered that all/most of the files were no longer readable by any of my macs. I seam to remember having similar problems like this while back, and finding an apparent link to my choice of format, so I ran diskutil list in terminal: /dev/disk3 (external, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *134.2 GB disk3 1: EFI EFI 209.7 MB disk3s1 2: Apple_HFS my-old-files 133.9 GB disk3s2 And I tried ls -l total 3858320 -rw-r--r--@ 1 kipbits staff 3430100 Nov 21 2016 2015-12-24.pdf drwxr-xr-x 8 kipbits staff 272 Sep 26 2016 2016-sep-14-files -rw-r--r-- 1 kipbits staff 25642888 May 18 2015 myold.mp4 -rw-r--r--@ 1 kipbits staff 884 Jul 31 20:20 someold.txt -rw-r--r--@ 1 kipbits staff 1320157184 Sep 21 2016 someold.iso drwxr-xr-x 4 kipbits staff 136 Sep 27 16:23 anotherdir -rw-r--r--@ 1 kipbits staff 626214959 Nov 5 2016 someold.mp4 drwxr-xr-x 14 kipbits staff 476 Nov 2 2016 sept2016files I think this looks normal? The problem is, I'm not able to open any of my files. I get the following errors: pdf: **The file “some-old.pdf” could not be opened.** It may be damaged or use a file format that Preview doesn’t recognize. txt: 800 byte files are blank rtf: **The document “some-old.rtf” could not be opened.** mp4: **QuickTime Player can't open "some-old.mp4".** To see if additional software is available that will enable QuickTime Player to open the movie, click Tell Me More. dmg, iso: will mount but did not test further pkg: **The operation couldn’t be completed. (com.apple.installer.pagecontroller error -1.)** Couldn't open "some-old.pkg" I found a thread on apple saying "*The partition map type doesn't really make any difference for non bootable volumes*", although i don't get any of these problems when using Master Boot Record & ExFAT. None of the files are more than a couple years old, so i don't think there should be any compatibility issues, and none of the files were corrupted when I copied them to the drive. I have had this same problem with other drives, and they were perfectly usable after reformatting, although this involved erasing files. My question is: **Is there a way to recover my files?** The file-sizes still display that the files are there. Is there a way to save these files and make them readable? ...Also, if it makes any difference, I am using El Capitan(for dev purposes) > **Update------------------------------------------------------------------------------------------------(04/Oct/2017)** I did a hexdump for some of the files in question. my output was something like this: 0000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 * 0000370 00 00 00 00 0000374 what does this mean? do you think a recovery app could even help me here? here are some threads that are perhaps related: ...Also could this possibly be related to SIP? I first noticed this problem around when i first upgraded to El Capitan. Or perhaps there is something else going on? I have recently been experimenting with windows and various forms of linux, and have been moving files around with thumb drives. Perhaps I plugged one in to the wrong computer and corrupted all the files? Whatever the cause, I'm wondering if the files might still be recoverable? Is hexdump a good way to diagnose recoverability? **Would buying a recover app just be a waste of $100?**