To prevent this inconsistent data entry, you can start a document in your word processor that records those data entry rules you set up for yourself. That way thay are all in one place and you can refer to them any time you wish. If you want, you can record them in some generally accessible place right inside of your database program. The point is, you need to record those self-imposed rules so you can be consistent through time as you enter data.
Here are some other instances where you may have made some unique data entry decisions you should record: How do you handle name changes? How do you record alternate names? How and where do you record conflicts in information between two sources? How do you record complex family relationships like illegitimacies, adoptions, non-married partners, etc. You get the idea.