hm what do you mean you have a few more files to add...? You didnt include all datafiles in your create control file statement? Well it is too late now to add because the file headers have been updated with new SCNs. You will get errors if you wanna add.
Archive log allows you to recover until point of failure (as long as you keep the archived logs)
With no archive log you can only recover until last cold backup, if your last cold backup is from 1 week ago then you would lose 1 week work.