The QNAM values that appear in various examples published in the SDTMIG and TAUGs have sometimes included the domain code, and sometimes not. The SDTMIG Appendix for Supplemental Qualifiers Name Codes (i.e., QNAM values) states that “the 2-character domain code is not required” although the QNAM values listed for general observation class domains do include the domain code.
The CDISC Non-Standard Variables (NSV) Registry Team has been cataloging the NSVs (aka supplemental qualifiers) and has proposed that, for supplemental qualifiers used with general observation class domains, QNAM should include the domain code. If the NSV were ever "promoted" to a standard SDTM variable, the QNAM value could be used as is, while a QNAM value that did not include the domain code would have to be modified. This naming convention also prevents potential confusion if the first two characters of a QNAM were not intended to be a domain code but corresponded with a domain code in a current or future version of the SDTMIG.
The only domains other than general observation class domains that can have supplemental qualifiers are Demographics, and in the forthcoming SDTMIG v3.4, Subject Visits. Standard Variables in the DM domain generally do not start with DM (the exceptions being DMDTC and DMDY) and Supplemental Qualifiers for DM have also not started with the DM prefix. The Demographics Supplemental Qualifiers included the population flags that were retired in SDTMIG v3.3 and supplemental qualifiers in examples, such as RACEOTH (Other Race) and RACEOR (Original Race). Starting QNAM values with DM for Supplemental Qualifiers to the Demographics domain is not necessary. Subject Visits is a somewhat different case. Other than STUDYID, USUBJID, VISITNUM, VISIT, and VISITDY, all variables in the SV domain specification start with the SV prefix, so it makes sense for Subject Visits Supplemental Qualifier names to start with the SV prefix.