Having translated a lot of Fraktur, I confidently suggest ‘I.J.G.’ is mis-transcription from the Fraktur script that was standard until 1941, I believe. It should be lower-case L, upper-case I.G. In Fraktur, to the untrained eye that could look like I.J.G. And A.V.J. is likewise a mis-transcription of A.V.I., = ‘Ausbildungs’, ‘Vorschrift’, ‘Infanterie’.