Theme: Cloud-hidden, whereabouts unknown.*
20. Old Glory: AMERICAN FLAG.
28. "Don't incriminate yourself!": ADMIT NOTHING. Good advice.
44. 1983 Lionel Richie #1 song: ALL NIGHT LONG.
9. With 65-Across, it has a 54-Across, so they say: EVERY.
65. See 9-Across: CLOUD.
54. Upside of 9-Across/65-Across ... and, chemically speaking, what each pair of circles represents: SILVER LINING.
I loved EVERYthing about this puzzle. Looks to be Jared's debut at the Corner. Theme-heavy, with lots to appreciate, including lots of artistic references. AG is the chemical symbol for SILVER (from the Latin word "argentum" meaning "silver"), flanking (or lining) three long answers.
*Van Morrison quotes the poem Searching for the Hermit in Vain, by Chia Tao (777-841) in his tune Alan Watts Blues. Watts includes the poem in the intro page to his book Cloud Hidden.
1. __ media: MASS.
5. Last year's frosh: SOPH.
14. Bug bite symptom: ITCH.
15. Indonesian boat: PROA. New word for me.
16. British prime minister before Brown: BLAIR.
17. "Cooking From the Hip" chef Cat __: CORA.
18. Prilosec target: ACID.
19. Well-manored men?: LORDS. Great clue.
23. Pigs and hogs: SWINE.
24. Nov. voting time: TUES.
25. Dead heat: TIE.
31. Platters from the past: LPS. LP = Long Playing, refers to the 10- or 12-inch diameter vinyl records, popular again. Any collectors here?
34. "Otello" baritone: IAGO.
35. "__ and Louis": 1956 jazz album: ELLA. Speaking of LPs ...
36. Marjoram kin: OREGANO.
38. Like the Constitution, 27 times: AMENDED.
41. "Unforgettable" father or daughter: COLE.
42. Nerve cell transmitter: AXON.
43. Sci-fi extras: ETS.
49. Guitar great Paul: LES.
50. Bring in: REAP.
51. New, to Neruda: NUEVA. Neruda was born and died in Chile, and wrote his poetry in Spanish.
57. Storage towers: SILOS.
60. City on its own lake: ERIE.
61. Morally repugnant: EVIL.
62. Fill with delight: ELATE.
63. Pie containers: TINS.
64. "La Dolce __": VITA. Italian for the sweet life. Also the title of a 1960 film by Frederico Fellini.
66. Ford contemporary: OLDS. Olds Motor Vehicle Co. was founded by Ransom E. Olds in 1897.
67. Eden exile: ADAM.
1. Layered silicate: MICA.
2. Tiny physics units: ATOMS.
3. Threaded hardware: SCREW.
4. Islamic law: SHARIA.
5. Guy who is out of this world?: SPACEMAN. Not Superman.
6. Killer whale: ORCA.
7. Indicate with an index finger: POINT TO.
8. Lived it up: HAD FUN.
9. Online marketing technique: E-BLAST.
10. YouTube journal: VLOG.
11. Musical gift: EAR.
12. Relieved (of): RID.
13. Trips around the sun: Abbr.: YRS.
21. Gandhi's land: INDIA.
22. Early-to-mid-August baby: LEO.
25. El Niño feature?: TILDE. Love this clue.
26. Shoreline recess: INLET.
27. "Jeepers!": EGADS.
29. "May __ now?": I GO.
30. Lady bird: HEN. Another great clue. Also a 2017 film.
31. From this area: LOCAL.
32. Humble worker, briefly: PROLE. Another new word for me, "a member of the working class."
33. Succeeds commercially: SELLS.
37. Bk. with the ark story: GEN.
38. Rocker Rose: AXL. Also Eddie Murphy's character in the 1984 film Beverly Hills Cop.
39. Like a particularly dark sky after sunset: MOONLESS.
40. The blahs: ENNUI.
42. In imminent danger: AT PERIL. Sounds odd - usually hear IN peril.
45. Opened or closed, as a lens aperture: IRISED. If you say so.
46. Hairdresser's goop: GEL.
47. Must: HAVE TO.
48. Swiss convention city: GENEVA.
53. Soul singer Baker: ANITA.
54. Annual Jan. speech, in Twitter hashtags: SOTU. State of the Union.
55. Orange skin: RIND.
56. Flashy rock genre: GLAM.
57. "Wait a __!": SEC.
58. Under the weather: ILL.
59. Poet __-tzu: LAO. "Music in the soul can be heard by the universe."