Paolo,
According to Nico Van Jijn, interpreting from his famous collection of original Luger engineering drawings and patent records, the concentric ring magazine was produced to physically differenciate a 9 mm pistol from a 7.65 mm as a safety measure. They were not exclusively or particularly for the Navy.
But to me more direct in answering your question, there doesn't seem to be any definite cut over time frame or serial number range that I have observed. In fact, I have a 1920's era '06 commercial that has concentric rings and is marked "Germany".
My supposition, and it is pure speculation, is that as the demand for small arms and their accessories increased, numerous subcontractors were called upon to produce magazine bottoms. DWM, I would suppose again, simplified the design for increased producability and added additional subcontractors while continuing to receive and use stocks from the original subcontractor, thus achieving simultaneous usage of both styles. Again, all of this is purely supposition on my part.
Tom A