Hi Peter,
Indeed, gear trains are strange things.
I have never made the calculations, but it may well be a couple of thousand revolutions before the marks line up again.
If all the gears would have the same diameter and the same number of teeth, then the marks would line up at every revolution.
But, let's say you have a 20 teeth gear meshing with a 100 teeth gear, the same teeth would line up every 5 revs.
If you change this to a 21/100 the same teeth would only line up after 100 revs, and to make matters more complicated, there are 3 gears in the the timing game, all of different diameter and number of teeth.
What counts is the number of turns the camshaft makes according to the crankshaft, and it's position to the crankshaft.
The gear markings are just there to get you started.
Have fun!