N-400 Receipt Number on Checks

My check had a payment processing number on back side that began with SSC which was different from the official processing number that was on NOA. However, the pre processing number also appears on far bottom left hand corner of my NOA. Mind you this was before they implemented the lockbox process so things may have changed.
 
I think things are a little different with the lock box, since I'm not seeing anything on my canceled check that screams out receipt number at me.

My receipt no. was handwritten in the upper left hand corner (right above my name and address) of the canceled check. However, things may have changed, since I applied long before the lockbox procedure was implemented.
 
My canceled check had many numbers printed on it but none of those matched my receipt number.
 
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