We do have an OEM license. Ig I understand correctly, we do not have to create an activation code for each customer system when we are using enhancer.
As we want to ship a standard database with the system which was created before having the OEM license and before adding enhancer to our maven process, I want to know if the OEM license is in this case works correctly.
That is correct. As long as you distribute your software with entity classes that have been enhanced by the Enhancer in OEM mode (i.e. with an OEM activation key), your software can access ObjectDB database files without the free edition restrictions.
Any ObjectDB 2.x database file can be used (including a database that was created before purchasing the OEM license), since the database file format is the same and it is not affected by having or not having a license.