MTBLS688 (IT-TOF): LSS Raw Data storage missing entirely, not just empty

[Nathan-D-R]

Summary

All 2149 files in the MTBLS688 accession (a 76-species medicinal
plant extract LC-MS survey, IT-TOF instrument) lack the LSS Raw Data
top-level CFBF storage entirely - not present-but-empty like every
other IT-TOF file in the corpus (MTBLS432, PXD025121, PXD020792),
just absent from the directory listing outright.

Found incidentally while widening the corpus for #20 (see CORPUS.md
Limitations and the corpus note at the top of
docs/format/04-lcd-chromatogram-pda.md).

A smaller, possibly-related data point: 1 of 20 MTBLS14423 files also
has no LSS Raw Data storage (the other 19 have it present but empty);
that study also cross-references a non-Shimadzu instrument for part of
its method, so that one file may be mislabeled or differently-sourced
rather than the same phenomenon.

Why this matters

crates/openszraw's current reader logic doesn't check for
LSS Raw Data's presence at all (PDA/LSS support isn't wired in yet,
see #2), so this doesn't break anything today. But once #2 lands
decode support, the reader will need to treat a missing LSS Raw Data
storage as a distinct, valid case (no chromatogram data available) -
not an error - and it's worth understanding why an entire accession's
worth of IT-TOF files omit it, in case it correlates with a
LabSolutions version, acquisition-software setting, or instrument
firmware revision that's independently useful to document.

What to try

• Compare File Property/File Property Original or other
  version/metadata streams between MTBLS688 and the existing IT-TOF
  accessions (MTBLS432, PXD025121, PXD020792) for anything that
  correlates with the missing storage (LabSolutions version string,
  acquisition date, method template).
• Check whether MTBLS688's files share some other structural
  difference already noticed but not investigated (e.g. absent
  PDA 3D Raw Data too, or a different set of top-level storages
  overall) - a quick olefile top-level listdir() diff against a
  known-good IT-TOF file would answer this fast.

Constraints

Clean-room only, per CONTRIBUTING.md: public dataset sources and the
existing local corpus only, no vendor software or SDKs.

Done means

A documented, evidence-based explanation for why these files omit
LSS Raw Data (version/setting/instrument-driven, or genuinely
unexplained after a real attempt), recorded in
docs/format/04-lcd-chromatogram-pda.md or docs/format/01-ole2-container.md
as appropriate, plus a note on what the reader should do when the
storage is absent versus empty once #2 wires in LSS support.