When running a FullTextSQLQuery - it will fail to bring back any columns that are not populated. So, for example, if the crawl didn't detect any PublishedStartDate's were populated - it wouldn't allow you to retrieve this column for anything. Is my understanding correct? And if so, is it possible to 'index' (may not be the right word) these columns in order for my query to run if they are all nulls. If not - I'll have to handle the exception from when I call the FulTextSQLQuery in order to code defensively which isn't really ideal.
We get the same issue, and the only way to index a metadata column was to create a fake document and run a crawl on it to be able to use it.
According to the dev team of my company, it was the only way we find to solve this. Sorry.