The way that I have done this in the past is to put placeholders in the content calendar & having a status associated with them (Not Started, In Production, Scheduled) and use the color associated with the single select status field to be my display in the calendar.
I would name the placeholders something like BLOG: TBD & when that blog is in production I would rename it & change the status to either “In Production” or “Scheduled” so that in the calendar I could see everything color coded appropriately, OR filter out scheduled/in production tasks.
Christine