Extending My Number Card when all the space is filled out?

I recently submitted a zairyu card renewal and went to the city hall to get my My Number Card extended again.

This time around, all of the four lines on my My Number Card were filled out.

How the city hall worker did it this time was she handwrote in the new validity date in the “電子証明書の有効期限” (“electronic certificate” expiry date) section, then told me I’d have to apply for a new My Number Card from scratch once my new zairyu card is issued.

Is that really how it works? It takes a few months for a new My Number Card to be issued, so I’ll be without a working card for a few months?

by acomfysofa