Recommendation N°21 not implemented?

[JoeyL-pf]

if unitcode from Rec. N°21 is used for quantity code

<ram:IncludedSupplyChainTradeLineItem>
    <ram:SpecifiedLineTradeDelivery>
          <ram:PackageQuantity unitCode="CT">4.0000</ram:PackageQuantity>

ZUV returns:

 <error type="4" location="/*[local-name()='CrossIndustryInvoice']/*[local-name()='SupplyChainTradeTransaction']/*[local-name()='IncludedSupplyChainTradeLineItem'][1]/*[local-name()='SpecifiedLineTradeDelivery']/*[local-name()='PackageQuantity']" criterion="document('zugferd2p0_extended_codedb.xml')//cl[@id=9]/enumeration[@value=$codeValue9]">
>         Wert von '@unitCode' ist unzulässig.</error>

Maybe Rec. N°21 isn't implemented? I used a official example from ZUGFeRD

zugferd_2p0_EXTENDED_Warenrechnung.pdf