
I have 40 or so Seikos and I have cards in all states and conditions - empty, filled, partially-filled, etc. Notice the warranty card clearly says they will keep it if you do have service.
I have service receipts from Japan, from CoServe in the US, and from aftermarket stores, and I think the card or a dealer's sales receipt (or both) will get you service in most instances with Seiko. Or you can return it to the store where the first buyer bought the watch from, if you know it. They can help you.
But warranty service is only one thing and if "flipping" a watch is your thing, you might want flawless documentation. I've only had one watch serviced under warrant - a Maurice La Croix. I was probably 3rd owner in 6 months, but had all the paperwork. It was fixed in 2 weeks, no problems at all.
Paying for service is another thing entirely.
Being willing to pay and then being refused service is extraordinarily irritating, and not unknown if you get a small-volume Swiss watch and can't account for how you got it.
Or if you have a nice used Rolex, for example, and want a service and to change a day wheel from one language to another. No can do, they said. In writing.
Or if you have a Swiss quartz watch and want a first-time battery replacement and are quoted hundreds of dollars from the authorized dealer ...
Alas ... Watches