Yes. It does look like LAST_UPDATED is actually required, at least for the batch process of updating the index statistics. That batch process is responsible for updating the min and max dates of the index as seen in EMERSE when searching without constraining on date. (The date constraints are actually applied to the CLINICAL_DATE / ENCOUNTER_DATE.) Sorry that wasn’t in the documentation as a required field, we can add that.
As for (2), yes, it should match the DOC_FIELD_EMR_INTENT value. If you loaded it as RPT_DATE, you could just change the DOC_FIELD_EMR_INTENT table instead. (That table is intended to make the field names in solr remappable.) (See http://project-emerse.org/documentation/data_guide.html#truedoc_field_emr_intent-table for more details, though I’m guessing you’ve seen that page already.)
As for (3), we assume you do have an encounter date for every note in Solr, but (just from looking at the code), it looks like there’s a chance it’ll work even without them. Such documents should never be returned from any search that constrains on date, but if you leave that filter open, I believe they should appear. However, we rely on that field for sorting, so either they may be out of order, or that part of the system might break. Like I said, we’re expecting all documents to have an encounter date. Setting it as a dummy date should work.