Hi Jane,
Sorry for late response. I am not aware of any specific standard requirements or guidance on handling interim data cut in SDTM data.
The only recommendation would be to use SDTM 3.1.3+ versions. RFPENDTC variable can be useful to provide Data-Cutoff date for each subjects.
Also, there is special Parameter in Trial Summary domain: DCUTDTC - Data Cutoff Date
Kind Regards,
Sergiy