How can I change duplicate values in a column based on the value in an another column?

Thanks so much for the quick reply!

The first attachment was a basic example, but the actual document is more complex (attached)

The style codes and colors come from our suppliers and will change for every brand and season so this cannot be a pre-defined list.

Each digit of the attribute section of the SKU is generated from VLOOKUP's against variable drop downs, with additional IF formulas supporting other functions we need the SKU to fulfill, so there would be too many possible combinations to split the input and output in this way

Once the attribute section of the SKU has been generated by the existing formulas, I need excel to recognise duplicates in the resulting values, but only add the sequential number at each change in the unique style code to avoid create individual SKU's for each size

Not sure I'm explaining this very clearly, but hope you can help!