#document-library 3 articles

• StorageMetrics lies two ways — all zeros, or plausible numbers from an older stategotchas / rest-apizero = not calculated, but non-zero can be stale (261 files / 3.1 GB vs real 794 / 9.5 GB); trust it only when TotalFileCount exactly matches the files you counted
• Created/Modified on a document library won't stick — and the API says 200 while ignoring yougotchas / listsA plain MERGE reports 204 and SharePoint overwrites both with "now"; ValidateUpdateListItem + bNewDocumentUpdate is the only path that holds, it wants the web's locale format (the error message tells you which), reads…
• Gallery cards render from tileProps, not from formattergotchas / listsThe documented top-level formatter is ignored; the card lives in a nested, undocumented tileProps.formatter. Layout and card must go in two separate writes (PnP or REST/SPFx)