Looks like the first gets run as:

for '0001' .. '1999'
[download]

the second as:

for '0001' .. '1999'
[download]

and the third as:

for '0001' .. '\'1999\''
[download]

So far as perl is concerned, it's then just a matter of understanding why those three renditions (well, two renditions actually) produce those outputs.

Here's the script I ran:

use warnings;

for('0001' .. 1999) {print "\r$_"}
print "\n";

for('0001' .. '1999') {print "\r$_"}
print "\n";

for('0001' .. '\'1999\'') {print "\r$_"}

__END__
Outputs:
1999
1999
999999
[download]

(Btw, there's also an anomaly in your subject line ;-)

Cheers,
Rob
UPDATE: Corrected my assessment of what the first rendition did. Originally I said it was doing for '0001' .. 1999 which is incorrect - as can be seen by doing a Devel::Peek::Dump($ARGV[0])