Although it may seem like a one letter or number difference may be close enough, it will most likely cause the part not to fit the application (or even be the same part.)
We can use control arms for a 2014 BMW 335i as an example:
31126852991 is the part number for the front left control arm, whereas 31126852992 is for the front right. In this case, these numbers are very similar, because they are side-specific though they're completely opposite of each other.
Now let's use a 2015 Audi A4 as an example.
"8K0698151K" is the correct part number for a specific VIN's front brake pads. "8K0698151H" seems close enough by just ending in "H" instead of "K", but they are for two different applications and not backward compatible.
If you'd like to know which parts are correct for your specific vehicle, please enter your vehicle information on fcpeuro.com underneath "Select your Vehicle". Simply enter your Year, Make, Model, Submodel, and applicable trims. Once your car is selected at fcpeuro.com, our catalog is automatically filtered to show parts that fit your specific car.
Once your car is added to the selector, there are a couple of important ways that we advise correct fitment.
The first is the "fitment indicator" shown on the Product Page after selecting a part. This box is below the "add to cart button" and has two states. It will either say " Yes this part fits" or "Part may not fit, click to verify".
Sometimes the green box will be accompanied by extra fitment notes. These notes may be independent of the information gathered by the vehicle selector. IE: VIN-specific options, need to be taken into account when determining overall fitment.