Nice Luger you got there.
The "44" are the last two digits in the serial number and are supposed to be stamped on most of the orginal parts of the pistol. Yours seems to be "match numbered".
The proof mark on the last picture indicate that your 1910 was send back to the factory in 1913 to have the hold open added. The German army did�´nt want the hold open at first but they changet their minds in 1913 and had it added in most of the previusly made pistols. Thei also had the front sight changed at the same time and the front sight base should also have similar stamp.