Nissan Altima manufactured 06 0f 01 I bought it for my wife's aunt put a starter in it worked dine for about a month then quit working . The starter is spinning but not engaging which is why I replaced it so I'm wondering what's causing the starters to go bad?
To directly answer your question, the model year (MY) of the car depends on the manufacturer's whim as to when they will start manufacturing the next MY. If your (or her) title states it's a 2001, then that's what it is, regardless of when it was manufactured. Nissan might do it in September, while GM might do it in July. It's all up to what they wanted to do. Since it appears Nissan did a model change between 2001 and 2002, they will usually start the MY later in the year because they have to change tooling, manufacturing, assembly lines, & parts manufacture. It's a lot harder going from one year to the next.
I'd agree with @Sherman418 as far as part of what was stated ... I'd suggest the starter has gone bad. Get a replacement and go from there. You can get OEM starters which would only last a month. Aftermarket "rebuilt" starters most likely have a longer warranty on them then OEM ones from the dealership. Also, for me, the cost difference, especially on something more expensive like a starter, would justify getting an rebuilt one versus OEM. Sometimes it just isn't worth it (IMHO). Since you've already bought the aftermarket starter, it won't make sense to go buy a new one, especially when you can most likely get this one replaced under warranty.
If it worked for a month, it was most likely the correct one for the vehicle. Looking at the starters for the 2001 and 2002, they are completely different for the 4-cylinder engine, and they didn't put a V6 in the 2001, so if you bought for a 2001 4cyl, it's the right starter.
While it is somewhat a whim as to when an OEM starts manufacturing/selling the next model year, there are a few rules:
The earliest date an OEM can legally sell the "next" model year is January 1st of the same year. In theory in about a month, on January 1st 2019, those vehicles sold on that date forward can be labeled on the 10th VIN digit as "The new 2020 Model Year".
Manufacture of a specific model year must end on December 31st of that same year. Building on the last example, a 2020 Model Year vehicle cannot be labeled as such past December 31st, 2020. You can't build a 1969 Ford Cobra now, although a certain automotive celebrity tried to do just that. The MCO "Manufacturers' Certificate of Origin" cannot be issued for prior years.
The second part is relatively meaningless, as I can't imagine why an OEM would label a vehicle as a 2020 when it's perfectly in their rights (since January 1st of the same year) to declare it the next model year, i.e. 2021. Unless you are sneaking to create a priceless classic car out of thin air and rusty steel, by forging MCOs.
Similar to this, is that the purple one you bought yesterday that was sitting on the dealer's lot for 16 months cannot be "remanufactured" or "re-VINd". It MUST be registered according to the model year declared by the 10th digit of the VIN, regardless of when it was actually sold.
It used to be new year models started in the previous Fall, perhaps September. But as Paul suggested, the "new" model year may have significant body styling/engine/layout changes, for which the tooling and logistics might not be ready until mid-year. Typically an OEM starts a new model year with a new vehicle, which is distinctly or at least somewhat different than the previous model year. That distinction is often a sales/marketing ploy, but often could be driven by manufacturing and parts source readiness.
Still, legally, in about 28 days OEMs have the ability to declare a vehicle to be sold on January 1st 2019 or later as a 2020 Model Year!
As silly as that seems, it's best to look at the driver's door or door jam FMVSS sticker, where the actual month and year of manufacture must be declared. This must also be compliant with any emissions label(s) under the hood or near the engine. The "model year" can be decoded from the 10th "digit" of the VIN, but keep in mind this has little bearing on the actual month or year of manufacture based on the above rules.
The FMVSS information is ALWAYS what you use to order parts. There may be mid-year changes, parts changes, etc. that mean a June starter won't fit the [new improved, hoping they don't crack like they used to, with the new "bendix"] July mounting flange.
When you order parts from a Dealer, they order by VIN, and the system knows which side of a cutoff is appropriate (if there is one). From a local parts house, you are best knowing the month and year from the FMVSS decal.
"Bendix". I have officially dated myself, and not in the fun way.