I finally got a chance to do some more digging. Turns out my file manager, Nemo, (Linux Mint) uses GVfs which mounts SMB shares via
/run/user/1000/gvfs
but not statically nor with appropriate permissions to torrent TO that location. So I made entries in fstab to /mnt but was still having issues before realizing that for permanent shares /media is the correct directory. Once fstab reflected those changes, I appear to be humming along nicely.
//bigboy.local/shows /media/shows cifs credentials=/root/.smbcredentials,iocharset=utf8,vers=3.1.1,file_mode=0777,dir_mode=0777 0 0
//bigboy.local/movies /media/movies cifs credentials=/root/.smbcredentials,iocharset=utf8,vers=3.1.1,file_mode=0777,dir_mode=0777 0 0
Permissions and fstab were the right moves - the tthing that threw me off was GVfs and how it handles smb shares upon user login. Weird.