OK. This is getting ridiculous. marto, just for you, I'm going to update this post with a bit of history on ftp. But, for now, please note; ftp does, and always has provided all the tools necessary to fairly accurately compare remote files, to local files. There has always been a wealth of commands available within the ftp command set. While you wait, you might look at the commands I've already listed, to imagine the possibilities. Here's another link to the same man page I posted 2 times prior, that lists the commands I've been referencing: ftp.
I'll be back... :)
UPDATE (as promised)
I had intended to write up a history on ftp, but for the purpose of this thread, the following link summarizes things quite well, I think. Please review:
Here's another link that includes a fuller set of commands: ftp commands
¡λɐp ʇɑəɹ⅁ ɐ əʌɐɥ puɐ ʻꜱdləɥ ꜱᴉɥʇ ədoH