A date written in an old book feels wonderfully direct. Unlike an estimate, it appears to announce its own answer. Yet the meaning of that date still depends on what the inscription records and how it entered the manuscript.
Record the claim before adopting it
Getty’s guidance on inscriptions and marks notes that inscribed information is not always straightforwardly accurate and that a manuscript colophon may be copied into a later version.
The practical lesson is to distinguish “the inscription states a date” from “this copy was certainly produced on that date”. The second claim requires interpretation of the first.
Keep wording and location together
In a reading note, record the source’s transcription or translation, its location in the object and the catalogue’s explanation. Do not move a marginal note into the main text simply because both appear in the same photograph.
If you cannot read the original script, identify whose reading you are using. That is useful provenance for your note, not a reason to pretend greater certainty.
Ask what event is being dated
Composition, copying, ownership and later annotation are different possibilities to investigate. Let the actual catalogue and scholarly discussion guide the question.
This connects with asking questions of primary sources. A direct piece of evidence becomes more useful when its precise claim remains visible.