Although some front plates in Germany do exist with no licence or technical inspection stickers on them, they are very rare.
Plates like these are almost certainly made-to-order specials and have never been on any vehicle at any time. Various German Ebayers sell plates like these at times and you need to be very careful as to whether it is a real plate or something that was made specially to make money.
Some of these supposed registrations cannot exist.
obamaforpres08 sold the mint, unused O 13 2410 but this is wrong for a diplomatic plate.
ennma sold the others with S-EX being a vanity type number.