Right now, "maint check-psymtabs" exists to check psymtabs, but there's no equivalent for the cooked index. This would be a good addition.
I have a patch that overloads check-psymtabs to do this.
Running this on gdb itself shows a lot of problems: (gdb) maint expand-symtabs (gdb) | maint check-psymtabs | wc -l 159122
I suspect my current patch is a bit broken since it also reports a large number of failures in Ada programs.