I am not sure I understood the request.
On emacs built from emacs-25 branch (could not verify the same on 24.5), by doing,
I get a very good explanation of how the backup files are named.
When Emacs makes a backup file, its name is normally constructed by
appending ‘~’ to the file name being edited; thus, the backup file for
‘eval.c’ would be ‘eval.c~’.
If access control stops Emacs from writing backup files under the
usual names, it writes the backup file as ‘~/.emacs.d/%backup%~’. Only
one such file can exist, so only the most recently made such backup is
Emacs can also make "numbered backup files". Numbered backup file
names contain ‘.~’, the number, and another ‘~’ after the original file
name. Thus, the backup files of ‘eval.c’ would be called ‘eval.c.~1~’,
‘eval.c.~2~’, and so on, all the way through names like ‘eval.c.~259~’
Should this bug be closed?