When we pull the oil plugs, we punch mark the location if it's not an engine we are familliar with, after all machine work is done it; gets another washing, blown dry and plugs are installed with either threadlock or locktite, I hate handing someone a bag of plugs when I know they have no idea what part of the block they came out of. some instances engines have o/ring seals - in that case we mark the oil hole with red or white marker, customer is told they are out and it is on the invoice.. alas still some forget to put them in, But they find that out when the PRIME the oil system <_<