Contacts does not edit any of your contacts automatically. The only thing it does is show suspected duplicates (e.g. same name, same info) in the duplicates tab, and at the top of your list when first detected, but it will never merge these automatically. You can have as many of the same person as you like, each with a different contact card. You can merge these contacts by going to the duplicates tab and merging them - you can choose which info to keep if there is two of the same info (e.g. phone number, email address), or you can keep both. Also, if you get new info shared to you, you can select "Add to Existing Contact" instead of creating a new card.