I'm assuming this is the right spot and that there's one maintainer for the configs.
1) For menu use, UI is preferred over DEFAULT, leaving default for its true purpose.
DEFAULT menu.c32
should read DEFAULT tc
UI menu.c32
I can provide more definitive reference (like syslinux:NEWS) if preferred.
2) tinycore-4.5.6.iso:boot/isolinux/isolinux.cfg line 4 references a non-existent label.
ONTIMEOUT plus
should read ONTIMEOUT tc
As a side note, there are some trailing spaces scattered throughout (since I happen to stumble upon with my editor mode due to using git which normally dislikes it).