GNU coreutils : backup option related to cp command

$cd  test-folder/
$>1
$>2
$>3
$ls
1  2  3
$cd ..
$>1
$>2
$cp -b 1 test-folder/
$cd test-folder/
$ls
1  1~  2  3
$cd ..
$export SIMPLE_BACKUP_SUFFIX=bc
$cp -b 2 test-folder/
$cd test-folder/
$ls
1  1~  2  2bc  3
$cd ..
$export SIMPLE_BACKUP_SUFFIX=.bc
$cp -b 2 test-folder/
$cd test-folder/
$ls
1  1~  2  2bc  2.bc  3
$