Been searching around and found this page... http://recordstoreday.com/CustomPage/6907
... containing a link to this spreadsheet...
http://download.recordstoreday.com/free/INDIE_EXCLUSIVE_STORE_SHEET.xls
Some release dates in the spreadsheet are listed as 2016, but clearly some are 2018 albums. Might not be directly related to RSD, need to look into it a bit more. Edit- yeah looks like an ongoing indie exclusive release list.