Vehicles may be 'quick added' from the product edit page with an ajax interface, this allows for a fast work flow.
The vehicles list can be browsed and managed from the control panel. This solves the problem of adding a vehicle by hand, or editing it. When you edit a vehicle, it will appear renamed under every product you've previously added it to. A make,model, or year can be also be easily renamed or deleted. If you delete a Make it will delete all Models,Years, and Product Applications.
If you have multiple spellings of something, it can be a very costly mistake, because you create significant issues with the user's ability to locate products. If they search on 'F-150' with a dash but your prodoct doesn't show up because your vendor put 'F150', the customer may not pick the alternate spelling. This is why merge was created, to consolidate alternate spellings & correct mistakes.
If you are inputting your fit assignments by hand you may need to assign a product to many individual fits. To speed up this process you can pick a top level attribute ( eg. make "honda" ) and have it add all the options ( models/options/years ) that are hondas. You could then go thru and uncheck any fits that do not apply. In this way you can map large collections of vehicles to your products.
In Magento you can duplicate a part, when you do this, all of that automotive product's vehicle applications will be copied over to the newly duplicated product.
The system can be set up to do year ranges, for instance if you want to be able to store "1991-2006" as an actual fit and apply all of those years to a product at once. Customers would then select the range of years that applied. Of course it can be called something other than "year". That implies it does not have to be a number, it contain letters and dashes in the year.