Theme: Parse the Reveal - Parse it correctly and you'll have the theme.
17A. Corporate world meal: POWER LUNCH
31A. Instruction on a Steinway: PIANO LESSON
48A. Political head: PARTY LEADER
65A. "The Maltese Falcon" actor: PETER LORRE
73A. CFO's monetary report, and a hint to this puzzle's four longest answers: P AND L. A profit and loss statement.
Argyle here and a couple of our regular Monday constructors.
1. Corrosive compounds: ACIDS
6. Dog in "The Thin Man" mysteries: ASTA. 1935 -1947 The movie series. 1957–1959 Two seasons on television.
10. Pork serving: CHOP
14. Heath-covered wastelands: MOORS.
15. Fish tempter: BAIT
16. What the little hand shows: HOUR. Digital kid, "What are hands?"
19. Otherwise: ELSE
20. Guys-only gathering: STAG
21. Lawyer: Abbr.: ATT. (attorney)
22. Artificial: ERSATZ. German Ersatz: a substitute.
24. Took a load off: SAT
26. Helps with the holdup: ABETS
28. Manning of the NFL's Giants: ELI. He was drafted as the first overall pick in the 2004 NFL Draft by the San Diego Chargers and immediately traded to the Giants. - Wiki.
36. Four times a day, in an Rx: QID. Latin, quater in die.
37. Early Peruvians: INCAS
38. Continental cash: EURO
39. Turn loose: UNLEASH
41. Fry cook's woe: SPATTER
44. Light bulb, in comics: IDEA
45. Motionless: INERT
47. CD-__: ROM. A Compact Disc used as a Read-Only optical Memory.
51. Obstinate beast: ASS
52. Back of the boat: STERN
53. Sky safety org.: FAA. (Federal Aviation Administration)
55. Historic Spanish fleet: ARMADA
58. Eden dweller: EVE
60. Rope source: HEMP
64. Aretha's genre: SOUL
68. Voice below soprano: ALTO
69. Defib specialists: EMTS. Defibrillation/Emergency Medical Technician
70. Disney mermaid: ARIEL
71. Burns or Byron: POET
72. Pair of performers: DUET
1. Bandstand boosters: AMPS
2. Small water bird: COOT
3. Nebraska neighbor: IOWA
4. Bottom-of-the-barrel stuff: DREGS
5. Ukr. or Lith., once: SSR. (Soviet Socialist Republic)
6. Touch the edge of: ABUT
7. "Oye Como Va" group: SANTANA
8. "__-Tac-Dough": TV game show: TIC
9. Walking obediently, as a dog: AT HEEL
10. 32 pieces and a game board: CHESS SET
11. Havana "Hi!": "¡HOLA!"
12. Force out: OUST
13. Chief exec: PREZ. Shortened forms.
18. Ancient Romans: LATINs
23. FedEx assignment: Abbr.: RTE. (route)
25. Capital of Samoa: APIA
27. Ordered (around): BOSSED
28. Provide with gear: EQUIP
29. Singer Ronstadt: LINDA
30. Thumb twiddler: IDLER
32. More in need of a rubdown: ACHIER
33. Kama __: Hindu love guide: SUTRA
34. Tiered cookies: OREOs
35. Societal expectations: NORMS
40. Reacts to being ravenous: EATS A LOT
42. Like better: PREFER
43. Big name in razors: ATRA
46. "No, No" Broadway gal: NANETTE
49. Since Jan. 1, on pay stubs: YTD. (Year To Date)
50. Jumped: LEAPED
54. Now, in Nogales: AHORA. Mexican state of Sonora or US state of Arizona, they abut.
55. Rush job letters: ASAP. (as soon as possible)
56. Caramel candy brand: ROLO
57. Volume-off button: MUTE
59. Flak jacket, e.g.: VEST
61. Whistle-blowing Brockovich: ERIN. Subject of 2000 film bearing her name.
62. Talking TV palomino: MR. ED. Yes, it is "Mister Ed" but TV is television.
63. __-mell: disorderly: PELL
66. Outback avian: EMU
67. Once around the track: LAP. Or what is formed from 24-Across.