Patents and patent applications are published with a two-letter code specifying the office that published it. Patents and patent applications with a EP code have been published by the European Patent Office while patents and patent applications with a national code (e.g. DE) have been published by the corresponding national office.
Like any other office, the European Patent Office only publishes applications that they received. As a result, an application filed at a European National Office will not be published with a EP code unless the applicant filed an application for the same invention at the EPO.
The set of patents and patent applications covering the same invention is called a patent family. Because the European Patent Organization adds a supranational route, there are many possible scenarios for a patent family to include EP and national members (e.g. DE or GR in your question).
Applicant filed an application at a national office (e.g. at DPMA in Germany) and this application is published with the corresponding 2-letter code. This first application provides applicant with the priority date.
Applicant filed a PCT application within 18 months, and this application is published by the WIPO (Worldwide International Property Organization) with a WO code.
Applicant designated the EPO from the PCT, and this application is published by the EPO with a EP code.
Applicant is eventually granted a European patent, published with a EP code. Applicant validates this patent in European national offices. Some of them will actually generate a code, yet this will not yield to a publication, unless the specification is translated.
Alternatively, applicant could first file at the EPO, and the application will be first published with a EP code, then file a PCT and eventually designate a European state.
Please note that the European route remains a non-mandatory, yet easier way to obtain patents in member states. Applicants usually prefer to file at the EPO as it is the easiest (and cheapest) route to get a patent in several EPO member countries, as there is a single prosecution, in a single language, etc.
Still, one could first file at the DPMA (and the application will be published with a DE code), then file another patent application for the same invention at the INPI, France's national office, and get a FR code.
Yet, several offices actually no longer perform search and delegate it to the EPO. Typically, this is what INPI does. Besides, with Unitary Patents and the Unified Patent Court, that have yet to enter in force, national routes will make less and less sense, except probably to get a cheaper priority date, as national offices have lower filing fees.