Shingle Overlap - Drip Edge

Good Morning ! I'm new on here. I'm a roofing salesperson.  Is there a standard for shingle overlap - drip edge ? I was taught there should be 1 inch at eaves and 1/2 inch on rakes. I also know there are roofers who do not overlap at all.  Thanks !  Any links would be appreciated as well.

Read the instructions on the packaging and go with what the manufacturer suggests.

Around here, the instructions are in both English and Spanish.  I may be one of the few who have ever taken the time to read them.