The unclued lights, all nouns or verb forms (one is a hyphened plural), include a common feature different in all twelve cases. Solvers are invited to indicate both possible unclued lights at 29 Down. Elsewhere, ignore two accents.

Across

1 Stab with a knife (5)

4 Order a gin around river (9, two words)

9 Potential difficulties from awkward Moscow and far North (10, three words)

11 Sad poem which its middle letters spell out (5)

12 Move forward and notice vehicle by church (7)

14 Corn produced by monarch reigning from 1714 (5)

15 Honda car going back and forth in town? (5)

21 Obscure eyepiece – artist’s...