Thank you so much for replying. Your help is much appreciated.
It had crossed my mind that the two dates could be for the reason you have suggested, and the fact that both that you and Ernst-Peter independently had a similar idea adds more weight to that possible explanation.
Landau (Hessen) rather than Landau (Bayern) also seems very plausible. However, I cannot find any record of a barracks (Kaserne) there at the beginning of the 20th Century. So perhaps he went there for a different reason, as suggested by Ernst-Peter. He was a butcher (Metzger) so not sure that he would have gone there for education/ professional development, but maybe for work?
With regard to the '1.8.1914' entry on the card, the dark line does seem significant and it is also a significant date. I wonder if it indicates that his father lived at that address on his own after mobilisation. But curiously that date is 'out of sequence' and is written in the upper part of the space available, as if it was anticipated that another date would be written below.
Thank you again for your thoughts