Why the same fact appears on every form
The examiner reads the bundle together, not document by document.
Your address appears on the application form, the guarantee letter and the residence certificate. Your income appears on the form and on the tax certificate. The marriage date appears on the form, the questionnaire and the family register. An examiner reads them together.
Most trouble in spouse cases is not about eligibility — it is about small inconsistencies. An address written from memory that does not match the 住民票 (certificate of residence). An income rounded up. A questionnaire that gives the ceremony date where the family register records the registration date. None is dishonest; cumulatively they make an account look assembled rather than lived, and they generate a request for further documents that adds months.
This is why the interview asks each fact once and writes it everywhere itself. Take the figures from the source documents in front of you rather than from memory, and the bundle will agree with itself.