I just noticed that a “gestation period” statement of “100±2 day” violates the “range” constraint of P​3063 (“0 to 5000”, without units), as seen here. I eventually realized why – we normalize values before checking the range, and 100 days means 8640000 seconds – but this confusing situation definitely needs to be documented on Help:Property constraints portal/Range and Help:Property constraints portal/Diff within range. (And then I suppose I should fix the constraint to add the “days” unit.)