I'd rather see invoices than stamps in a book as they could mean anything!
When I bought the Mondeo I had a list from LeasePlan telling me what was done, where it was done, when it was done and how much it cost.
The car doesn't have all it's stamps any more as I usually service it myself but I've stapled all the receipts together from services with a note on the front saying what was done and when it was done.