How do you adjust the shifter mechanism so that the number displayed on the shifter dial matches the gear that the bike is in? I have searched everywhere on the net to find this info and have searched this site but cannot find the answer. For some reason, after adjusting the rear derailleur on my wife's "Specialized" hybrid 21 speed bike, the dial on the shifter face won't line up with the correct gear that the bike is in. It shifts fine, goes into all 7 gears (sprockets) without grinding, does not slip off the small sprocket, and just seems to be working fine. Why is the gear position displayed on the Shimano ST-CT15 shifter not pointing at the correct gear position? Thanks in advance for any help.

Doubt you can adjust it.

What happens when the indicator won't move any further and you make another shift in that direction?

Nothing happens, it won't shift anymore because the chain is in it's highest or lowest position on the rear sprockets, but the shifter indicator is at the incorrect number.