The normal behavior when copying a field to another OrderForm is to create another field in the form and if there is a field with the same name it will not overwrite that field, instead, it will add a "1" after the name and keep both fields. If you are unfamiliar with that process it can be seen below.
In addition to the normal behavior when copying a field to another form, you can also copy a field and force it to overwrite any fields with the same name. This is useful if you have several forms with similar fields that all need updating.
This way you can update it once then copy that update to all needed forms which will replace the old information. The process is the same as above but you need to click the "Overwrite Existing Fields" checkbox to force the copy to replace any fields which can be seen below.