Glossary
MFT file reference
An 8-byte NTFS identifier combining a 48-bit MFT entry number and a 16-bit sequence number, stored in many ShellBags entries.
An NTFS file reference identifies one record in the Master File Table: a 48-bit entry (segment) number plus a 16-bit sequence number, documented by Microsoft as MFT_SEGMENT_REFERENCE. The sequence number changes when the record is freed and reused.
ShellBags file entry items carry the folder's reference in their 0xBEEF0004 block. Comparing it with the current $MFT and the USN journal shows whether a folder still exists, was renamed, or was deleted. See finding deleted folders with ShellBags.