Retirement tax questions

Thanks for the comprehensive reply!   I appreciate your effort regarding the advantages of a joint return, but there are some marital situations which just prevent doing so....no need to elaborate any further :(

However, with regards to filing - yes, a portion of my SS-only income IS taxable, but it's still below the $13,850 exemption - so I indeed owe no taxes.  You STILL say that not filing will be a red flag?