The VISI and PCMB subrecords are timestamps that can be decoded the same way the Version Control Info 1 subrecord is decoded.

They are compared against the VC Info 1 subrecord of precombined REFRs in that cell, and if the VISI/PCMB timestamp is older than the newest VC Info 1 timestamp for any precombined REFRs then precombineds and previs get automatically disabled for that cell.

I would recommend making the VISI and PCMB subrecords still be edited as hex, or use some method to keep people from putting an invalid value in those subrecords.