Glossary
Biome tombstone
The Biome tombstone folder holds SEGB files expired from a stream's local directory. Many parsers skip it, yet it can extend the activity timeline.
tombstone/ is a subfolder of a Biome stream's local/ directory, for example ~/Library/Biome/streams/restricted/App.InFocus/local/tombstone/. When SEGB files expire from the active stream, Biome moves them there.
The folder matters for two reasons. It can extend the timeline beyond the usual window, which is about 28 days for most streams according to iOS research. And it is easy to miss: mac_apt skips tombstone/ by default, and other parsers often do the same.
Collect the whole stream folder, parse tombstone files as ordinary SEGB files, and label their records so they are not confused with active ones. How long a file stays in tombstone/ is not publicly documented, so measure the oldest record on your evidence. See the Biome SEGB file format.