Date, eventdate, dateformatter

I don’t know if it’s better here or GitHub. I describe my problem and you tell me.
Since I switched to biblatex, I have problem to decide which fields I should use for date.
I discovered that date is automatically formed from year and month fields. I can export them with \date. But I have some discrepancies, depending the way month is typed:
\date \month
2015-10 Oct
2015-10 10
But since I want to personalized export to 10/2015, I need the formatter (since I can’t print correctly /month//year for case 1)
But it doesn’t export, because Jabref complains date is not complete.

ERROR net.sf.jabref.gui.exporter.ExportToClipboardAction - Error exporting to clipboard
java.time.format.DateTimeParseException: Text ‘2015-10’ could not be parsed at index 7

It seems #oct# is the correct way to write month (according to automatic cleaning), so it doesn’t help me.

My overall goal is to be able to use date close as eventdate was described in biblatex. Meaning, find a way to export as I needed, sometimes short, sometimes long with st/nd/rd/th. Eventually, be able to get a range of date (not supported yet).
This issue is mostly related to abstract/inproceedings types, not really for article.
Let me know what you think.
Thanks to read me,

Reference : 2.3.8 Date and Time Specifications (page 36)