You've understood it correctly. It is not only in Germany though, a large part of Europe uses conspicuity code A1000 for Mode S flight identification.
Basically there are 3 Mode A code allocation systems in use:
- Originating Region Code Assignment Method (ORCAM)
Aircraft are assigned a code on departure and will maintain this code until they fly into a region where their code conflicts with another flight. Then it is reassigned.
- Centralised Code Assignment & Management System (CCAMS)
A computer system allocates codes to flights based on the planned trajectory through the CCAMS area and ensures there will never be a code conflict.
- Elementary Surveillance (ELS),
If a flight needs to be (re-)assigned a mode A code and it is in Mode S radar coverage and the downlinked aircraft ID correlates with the filed flight ID on the flight plan, code 1000 is assigned. Mode A 1000 serves as a signal to the Flight Data Processing System to correlate the radar track to the flight plan based on the downlinked Mode S aircraft ID instead of the Mode A code. This method is usually used in combination with ORCAM, sometimes with CCAMS.
Google for 'Eurocontrol Aircraft Identification Programme Operational Concept Document'. Eurocontrol have a habit of changing their website paths every other month so I won't post a link, it will likely be dead before you click it.