BCA's FTP facility does not properly timestamp any files that you upload. This is because Pure-FTPd, which is what's running on BCA's server, does not properly understand the MDTM command.
When you upload a file from your PC, it is handy if the server can maintain the same "last modified" date that your file has on your PC. This means that your web pages will display a helpful "page last modified" date, if you are implementing that via a bit of PHP code (or whatever).
The "default" action of the server, when you upload a file, is to timestamp it with the current date. However, your FTP package can likely send an MDTM command which says "change the timestamp to the value I am sending". The problem is that Pure-FTPd does not take any notice of this command. I have found this frustrating, when importing files from another site or when I dont actually want to change the "page last modified" date.
On my caves.org.uk site, if my FTP package sends the command
MDTM 20110717010101 /public_html/.htaccess
it gets a response
213 File modification time set.
And it does, indeed, alter the timestamp on that file. Whereas, on the BCA site it gets the response
550 Can't check for file existence
It appears that Pure-FTPd does not support the widespread but "non-standard" extension to the MDTM command, which otherwise merely *fetches* the file modification time.