"...must be something with how the file name is built..."

Others pointed you to it already - but anyway, i put in my two cent:

host:~ # perl -MPOSIX=strftime -e 'print strftime( "%Y%m%d.csv", local
+time );' | hexdump -c
0000000   2   0   1   4   1   0   0   8   .   c   s   v
000000c
host:~ # perl -e 'print qx(date +%Y%m%d.csv);' | hexdump -c
0000000   2   0   1   4   1   0   0   8   .   c   s   v  \n
000000d
[download]

Best regards, Karl