Hi Gerry,
here the translation.
"Velten is a city with a big development area. The letter is likely to go to the postal detection service (the word is very german, sorry.. but this gets the meaning) and there all notification books (another typical german with no real translation) will be searched for this name in Velten. This can take some days til months. If there are different persons with the same name or the person is not living there anymore, the letter will come back as undeliverable"
I hope this helps, it actually only means, that sending a letter without the full adress can be quite risky in a city of a certain size. But I have seen that someone gave you the hint with the sms to the mobile.
Have a happy new year
Barbara