Many of our research projects have data items / artefacts with uncertain dates of provenance, this information can currently be recorded on Figshare at the moment using custom metadata fields to indicate 2 dates for a range.
However, discoverability is the issue, especially if a viewer of a collection was trying to narrow thousands of records down via year.
I'd accept you still need the 'Posted by' date and this would remain untouched, and I assume this would be achieved by having additional custom metadata fields which were date input fields.
Just thought I'd post an update on a thought I had on this subject (not wishing to 'solutionise!'). Following realising that you can have 'date' as a custom metadata field already, which means in theory it may then be easier to achieve this bit of functionality than first thought.
However appreciate, there are 2 key components that will result in us getting to where we need to be on this: