Defect vs. Discrepancy vs. Missed Requirement

evening all. How does your team handle these situations where the AC is vague/does not specifically list out all of the requirements while the work meets the AC's as they are written but not as the product owner expected? My team has the habit of calling these defects & adding work to the original ticket. Also, when does a discrepancy count as a defect? For example a story AC lists "the work should match the approved mockups". So we could have all of the elements in place but maybe a 1px discrepancy in the spacing between two elements, or a component looks like the mockup until the dynamic behavior of the web-page is activated / data loaded/ action triggered etc.etc. How should these cases be handled? The acceptance criteria does not list the spacing between individual elements as a requirement nor the behavior of dynamic UI elements etc.etc.