The unclued lights are of a kind and are listed together in Chambers 2011. Solvers should highlight two normally clued solutions which together form another theme-word.
 

Across

 
1    Ties series of games with instrumentalists (11, two words)
7    Small county’s struggle (3)
11    Clog has lost its tip – repaired clog (6)
16    Young lad from Nantwich, rising (5)
17    Number one difficulty in the Big Apple (6)
18    Old count makes school on time (5)
20    Dazed state from formal protest? Not half (6)
21    Salesman’s patter at station 13 (5)
22    Publishing what the petitioner is doing (7)
27   ...