Yes, and the main reason in our experience is earpad wear and tear.
Worn earpads tend to affect the frequency response of your headphones. Depending on the model, the change in response can reach 2-3 dB in certain frequency bands.
If your earpads show signs of wear (e.g. they are deformed and flat), we recommend replacing them with new ones before mailing the headphones to us for individual calibration. If you do change the earpads, your headphones will be calibrated with a brand new set on and you will always be able to return to the original calibrated sound by replacing the earpads.
Can I improve the Frequency Response?
In our experience of measuring over a thousand units, we haven't yet noticed any significant difference in frequency response (FR) between brand new and used headphone drivers (as opposed to speakers, where that is definitely a factor). The measurement process does involve playing a considerable amount of audio through the headphones, so the drivers are getting a good workout, we have not identified any faults that would result in FR change. We have used and tested premium cables and other improvements, and we cannot say that this brings a significant difference and/or improvements to the FR if we compare the two calibrations.
If you are considering purchasing our calibration services and want us to use your premium cables, etc. We can definitely make this happen, and encourage you to send everything to us in one package.