CLASS DEFINITION DRIFT
The category still has its name and no longer has its edges.
01 DEFINITION
Condition in which what a category covers changes gradually through use while its name stays fixed, so records made years apart carry the same label for things that were not the same kind.
02 CONDITIONS
UNCERTAINTY
UNRECORDED
Nothing holds what the category meant at the time a given record was made.
TIME PRESSURE
LOW
The movement takes years; no single moment of it is noticeable.
ERROR ASYMMETRY
DEFERRED
The drift costs nothing until old and new records are counted together.
OPERATOR STATE
SUPERVISORY
The person is reading across a history rather than working a case.
03 WHERE IT APPEARS
MEDICALA diagnostic category covers different presentations now than it did when the older records were written.
PUBLIC SERVICEAn eligibility category has been applied more broadly each year without being redefined.
FINANCEA product classification has widened through use while its name stayed the same.
INDUSTRIALA fault category now covers conditions it did not when the code list was written.
EDUCATIONA level descriptor has moved through years of application while keeping its wording.
LOGISTICSA handling category has drifted in scope and the historical counts are compared as though it had not.
04 WHERE THIS IS SURFACING
This surfaces wherever categories are old enough to have been applied by several generations of people. Nobody redefined anything; the edges moved by being used.
What stays unresolved is how a category records its own movement — versioning it makes every historical comparison a translation, and leaving it fixed makes the history look consistent when it is not.