Mislabeling, and the specimen that was wrong all along
Updated
A label can be intact, legible and false, and the collection has no way of telling you.
Two kinds of wrong
Wrong when written. A misidentification, a guessed locality, a dealer's optimistic attribution.
Right when written and wrong now. Species get redefined and discredited; localities get renamed, reassigned or shown to be something else.
The second is not an error by anybody. It is the reason a label should record the name in use at the time as well as any correction.
Species drift
Names are periodically reviewed. Species are split, merged and discredited, and material sold under an old name for decades turns out to be something else.
Varietal and trade names are the worst offenders, because they were never species names and were frequently invented to sell material.
An identification is worth recording with its basis: visual, a physical test, an instrumental analysis, or an authority's opinion. A label that says how it was determined ages far better than one that asserts.
Locality drift
Mines change name and ownership. Districts get redefined. Material attributed to a famous locality turns out to be from an adjacent one, or from a different country entirely.
Material with a locality that suddenly became fashionable is worth extra skepticism, because that is where the commercial pressure to relabel sits.
What to do when you find one
Do not alter or discard the original label. It is evidence of what the specimen was called and when.
Add a new label stating the correction, the basis and the date.
Record both in the catalog, with the old entry retained rather than overwritten.
And if you are selling it, disclose. A specimen with a corrected label and a clear history is worth more than one with a quietly rewritten one, and the difference is trust rather than stone.