awk variables don't work for date grep when start date and end date are in different months

zgrep -h -i "XYZ" ls filename* | sort -r | awk -v "b=Jun 14 05:39" -v "e=Jul 14 05:39" -F ',' '$0 >= b && $0 <= e'

This doesn't work

But zgrep -h -i "XYZ" ls filename* | sort -r | awk -v "b=Jul 1 05:39" -v "e=Jul 14 05:39" -F ',' '$0 >= b && $0 <= e'

This works

When I gave start date and end date from different months it doesn't work.

Is there something wrong in the way I've used the awk variables?