I’m having an issue with getting sharepoint to work correctly (the way I understand it should) with the RefinableInvariantDate property.

My sharepoint site stores project emails and I have a webpart for the users to search all the emails and get back the relevant ones in date order.
The items in Sharepoint have an emailsentdate property which is populated when the email is uploaded to sharepoint.
However, in some situations this can be null, in those cases I want to default to the Created date value.
My research led me to use the RefinableInvariantDate property, so I added mappings to both the emailsentdate and Created (CreatedTime) crawled properties, on the assumption that if it discovered emailsentdate was null, it’d then set the value to Created.
However, this doesn’t seem to be working, Sharepoint seems to crawl files until it finds a record without emailsentdate and then it just stops and doesn’t do any more.

I’ve tried re-indexing the site, I’ve tried re-indexing the Document Library, but it has not helped.

Any extra steps I could try would be greatly appreciated

Thanks