Maybe my english is the cause of misunderstood.
App is for single users that they want to keep logs, notes about their car service, insurance etc.
Example: i have 1 car and in the app i can enter all the information and obligations about my car. The date of last service, the date for the next service, date insurance policy starts and ends, date of tire replacement, next replacement, date of last refueling, prices of them etc. Like a car agenda. Like service book but with more "items". There is no need for more fields like vin or plate. All records are for my car. If i have 2 cars then i can separated them from the field "vehicle" (example: vw, audi, seat, polo, golf, or whatever user wants to write (free text)). Now, if user has 2 cars of the same brand he can separated them with text (ex. vw1, vw2, or polo1, polo2 etc).
That is also the reason that i think TinyDb is enough for that app.