Hi!
I've made a lot of good use of Wikidata for harvesting information about names in our database, including specific birth & death dates. But, when a specific date isn't known, & only a year is known, WD records that as January 1 of that year. I have to throw away any date that is January 1, as I can't be sure if it is accurate. I know there is a (rather awkward) way of recording "circa" for dates, but is there some identifier for an unknown date within the year of ____ that can be used?
Well, in Wikidata itself there is a precision accompanying the date - if the precision is "years", then you know you can discard the day.
In SPARQL database, the short time value[1] does not carry precision, so unfortunately there's no way to know from that value, but if you use full wikibase:Time value, again, you can use wikibase:timePrecision to know if the date is accurate or just a placeholder.
[1] https://www.mediawiki.org/wiki/Wikibase/Indexing/RDF_Dump_Format#Time