Only the last 38 bits come from the serial number. Because of the grouping explained above, these 38 bits are contained in the last 10 hex bits of the EPC. The 10 rightmost characters in the example above, 29-39-90-F4-1D, contain the 38-bit serial number (and an additional 2 bits from the Item Reference Number assigned by BioTillion). These two bits and all of the leftmost characters, 30-00-30-28-32-C2-18-4C-02, typically do not change from vial to vial. Thus, if a user would designate the unchanging part of the EPC (30-00-30-28-32-C2-18-4C-02 in the example above), by the letter Q, for example, then a short form of this particular tag ID can be written on a label as Q293990F41D which is only 11 characters long instead of 30-00-30-28-32-C2-18-4C-02-29-39-90-F4-1D which is 41 characters long.
However, it should be noted that the 30-00-30-28-32-C2-18-4C-02 part of the EPC could change if we introduce new tag types, for example. So any scheme intended to abbreviate the EPC should represent the left most characters with a known token. If the number represented by the "Q" should change, another token can be used instead of the "Q".