Another SS Spring Question

The part number for the left hand SS spring on my Duster is P3690457 and everywhere I look the part number for the right side *should* be P3690456....I just happened to have my head under the right rear spring, and the stamped number is P369045X....?

I can find a -454, -455, and -456 in the Mopar catalog, but no 45X, and my internet sleuthing didn't solve the mystery either. Any ideas where I can double check the specs on it?