One folder per cat, newest proof on top
Splitting the drawer by cat solves the most common filing mistake: certificates for two or three cats shuffled together, with one cat's booster mistaken for another's. Give each cat a folder of a different colour, label the spine and the front with the cat's name, and file that cat's vaccination certificates in date order with the most recent on top.
On the inside front of each folder, keep a simple cover sheet: cat's name, date of birth if known, microchip number, and a short list with each vaccination, the date it was given, and when the next one is due. That cover sheet is the page you actually read — the certificates behind it are the proof.
Reading due dates without hunting through certificates
Vaccination certificates list several components, and the due dates for them do not always match. On the cover sheet, write each component on its own line with its own next-due date, rather than a single date for the whole visit. That way a booster that falls due sooner than the others stands out instead of hiding behind a later, more memorable date.
When a new certificate goes in, update the cover sheet in the same sitting, while the vet visit is fresh. Cross out the old due date rather than erasing it, so the folder also shows the pattern of how regularly boosters have been given — useful history if you change clinics.
A drawer routine that keeps the system honest
Choose a fixed moment to check the folders — the start of each month works — and flip only to the cover sheets. Any cat with a due date inside the next six weeks gets a note in your diary or phone that day. The drawer check takes minutes because the cover sheets do the work; you never need to read a full certificate unless a date looks wrong.
Keep related papers in the same folder behind the certificates: microchip paperwork, insurance documents, and any letters about your cat's care. A folder that holds only vaccinations stays thin and tidy, but a folder that holds the cat's whole paper life, with vaccinations at the front, is the one you will grab in a hurry.
When a folder shows a gap
If a cover sheet shows a booster already overdue, or a certificate missing for a year you know a vaccination happened, contact your vet clinic and ask them to confirm what their record shows. Clinics keep their own vaccination history for your cat, and a short call usually fills the gap so you can correct the folder with confidence instead of guessing a date.
If a kitten joins the household, start that kitten's folder on the day the first vaccination record arrives, even if it holds only one certificate and a cover sheet copied from the breeder's or rescue's paperwork. Kitten courses involve several visits close together, and a folder begun late tends to reconstruct those early dates from memory, which is exactly where errors about what was actually given begin.
For a multi-cat household, that per-cat folder discipline pairs well with keeping each cat's vaccination dates in KinsLe's Pet Passport, so every cat's records travel as one tidy packet to appointments, boarding, and handoffs.