I really liked this puzzle and its wonderful construction.
Once the unclued down entry was discovered and the puzzle's title decoded the theme became clear.
I misinterpreted "successive" in the preamble, but when I was flummoxed as to how SIX DOUBLE clues could lead to FIVE thematic examples and a TWO-WORD description, I eventually had a PDM and all became clear, allowing me to reverse engineer the remaining double clues.
I also had a pleasant surprise when I came to highlighting — not called for in the preamble — the thematic entries.
Well done, Phi.
[Thanks, mattrom (#13), for your exposition on 14ac. This clue didn't really work for me. The BRB clearly states that "cattle" is a plural noun, so the word from which the "gathering" (new word to me) is to be removed doesn't really cut the mustard.
Conversely, my Classical background tells me that the 'Latin deity' in 11ac — part of a Roman double act — is, in fact, a plural noun so the surface reading of the clue is flawed.]