I have distributed a lot of sticks with testfiles among friends and colleagues for testing and the result is:
The renderer doesn’t matter - everything was played.
But the sorting of the files is absolutely important. Not only “old” devices are affected, but also many new ones. You really have to do it, if you want to have the greatest possible copatibility
“A file or directory on a FAT volume always has a short file name , which is the old MS-DOS 8.3 name format. It means that the name part of a filename must have at most eight characters, and its extension at most three. A file or dir can also have a long file name , which can be a bit longer than 250 characters, and supports Unicode characters. When a file name contains mixed case, or has one part that doesn’t fit in the 8.3 convention, the file has both - short and long filenames.” - quoted from http://www.anerty.net/software/file/DriveSort/ - and I also found DriveSort the best program to do this - we had to do this with 450 pieces.
And referring to gapless mp3. The explanation of @seablade is still valid - you cannot predict the gap between files. I have 18 tracks and some transitions had really no gap and some had 3 seconds, the rest was in between…