Apologies for resurrecting an old thread, but this is the only one that comes up if you search for SMT7921.
I recently ran into the same issue and reached out to KYB technical support to check if these are in fact real KYB parts. The set I received have the following part numbers on them:
KYB responded quickly and confirmed that
these are genuine KYB parts, and that the numbers we see match their internal stamping numbers.
Hopefully this helps others who run into this issue in the future.