GreyC,
Yes you are correct I can't really know for sure.
I base what I know on the pictures and dates I have, I deduced some information.
I know that my Great-grandfather was handed his Iron Cross on the 6.11.1916 I will attach the picture. That gives me the conclusion that on the pictures with Sick he is wearing the bar, it must be after that date. Presuming he wasn't part of the 163th before that, which is most possible.
In the nice article above of Christian Mack on Opa as Bursche: https://opaskrieg.de/de/opa-franz-der-bursche/ you find a quote.
"Jeder Bursche muss ein Jahr an der Front dienen und dient das zweite Jahr als Bursche. Ein Posten, der sehr gesucht ist. Diese Männer sind im Allgemeinen dienstfrei und werden nur dreimal in der Woche, entweder am Vormittag oder nachmittags „herangezogen“, damit sie nicht zu fett werden und nicht alles Gelernte wieder vergessen."
" Every Batman must serve one year in combat and the second year as batman. A position, that was highly sought after. These men are generally off-duty and are only engaged about three times a week, either in the morning or in the afternoon, so that they do not get too fat and forget everything they have learned."
So if I go by that; My great grandfather might not have been part of the 163th before that.
This pictures is from 14.8.1917,
Taken at the Command post of the 81st Infantry Brigade, Oberstleutnant Sick's Command Post.
My great grandfather in the background.
Hopefully I will find more information in the next few years.
thanks