Hi Sophie,
SD1251 rule is based on official CDISC rule CG0108 (EXVAMTU = null, when EXTRTV = null) for SDTM-IG 3.2. A CDISC source of this rule has a reference to SDTM Model rather than Implemention Guide.
EXTRTV, EXVAMT, EXVAMTU are standard variables only in SDTM-IG 3.1.3. However, --TRTV, --VAMT, --VAMTU variables are still in SDTM Models of all new versions. Therefore, these variables may be utilized in EX domain. In such case, SD1251 rule is applicable in all SDTM-IG versions starting 3.1.3.
I believe that a logic of SD1251 rule is very clear: “Treatment Vehicle Amount Units (–VAMTU) are applicable only if you provide Treatment Vehicle info (–TRTV)”. I would extend a logic of this rule by additional requirement for non-missing value of Treatment Vehicle Amount. User may use Units only if both name of Trt vehicle and its administered amount are populated.
Kind Regards,
Sergiy