Ericg #19
As the preamble states, 10 of the solutions start or end with an abbreviation (HINT: There are 7 different abbreviations) - all abbreviations are of a kind (ie are similar.)
The part of the solution that is the abbreviation (start or end) is not 'covered' by the clue - in other words the clue only 'points' to the part of the solution either following the abbreviation or preceding it.
So - MONAD has one definition in my OED as 'God';AD = Anno Domini, which is clued as 'after Christ' - so the part of this solution that is not 'covered' by the clue is 'Mon'.
Similarly 21d 'Sailor with personal problem' = BOSUN. A bosun is a sailor; BO is ...... and again the abbreviation is not 'covered' by the clue.
Looking at the 2 abbreviations in the above should give you the idea!!