"Has improper value for" is a predefined property to track input errors for irregular value annotations that was likely caused by type or allowed value restrictions.
en:Optional: A date supplement, like 'approx.', a season ('Summer'), a quarter ('1st Quarter'), or any other information regarding the publication date. //[RefMan 05: Y1,PY pro parte] +
Optional: A date supplement, like 'approx.', a season ('Summer'), a quarter ('1st Quarter'), or any other information regarding the publication date. //[RefMan 05: Y1,PY pro parte] +