Why would extinct be missing from /species/search?

related to Extinction status and the species API routes (can’t re-open that thread though)

The species API route /species/search gives extinction status for some taxa, but not others. Why might the field be missing for some taxa? For example:

curl 'https://api.gbif.org/v1/species/search?q=Camelops&datasetKey=d7dddbf4-2cf0-4f39-9b2a-bb099caae36c' | jq '.results[].extinct'
true
null
true
true
true
true
true
null
true
true
true
true
true
true
true
true
true
true
true
true

If the extinct field is a boolean, does null (missing) mean that it’s extinction status is unknown?

And I assume null's are simply dropped from JSON results before being returned to the client?

Yes exactly. NULL means we don’t know it and properties with NULL values in GBIF JSON are left out and do not use the Javascript null value

Thanks very much, makes sense