An enjoyable puzzle. I didn't know the Gone With the Wind quote, but I had enough letters to guess “childbirth”, and it happened to be the top Google hit for me for “childbirth quote”. As for the other... more on that a bit later.
The three unclued rows contain two part-quotations. A superfluous letter is yielded by the wordplay in each clue. Read in order, these letters complete the first quotation. The surname of the author of the second one should be highlighted in the grid.
- T 10ac: ACCESSORY: Additional trial involving difficult company cases: not entirely sure about the wordplay here; maybe TRY around *(CO CASES)?
- H 13ac: ORCA: Tolkein's ogre finally got away from old enclosed fruit garden: ORCHA(t); I think the definition is wrong, sadly.
- E 14ac: SPOOM: US elks retreating gathering power, scud before the wind: MOOSE (US elks) reversed around P(ower)
- R 15ac: SENNA: Nurse slipped back laxative drug: SEN (ref. State Enrolled Nurse) + RAN (= slipped)
- E 17ac: LAPSANG: Variety of tea, unlimited range after falling away: LAPSE (= falling away) + (r)ANG(e); ref. Lapsang souchong
- S 19ac: LIER: More secretive one who is incumbent: Double Definition (SLIER = more secretive; LIER = one who lies down)
- N 20ac: LOOK YOU: Welsh observe liberal sex with African fellow: L(iberal) + NOOKY + OU (South African slang for man)
- E 21ac: EATING: Consumption surprisingly negative, lacking value initially: *(NEGATIVE - V(alue))
- V 27ac: CACOON: Decrepit van with rotten coco seed: *(VAN COCO)
- E 29ac: PLAYERS: Actors' appeal not accepted in very long time: PLEA + YEARS - A(ccepted)
- R 32ac: TRON: Bishop among people who are in Lanark market place: RR (bishop) in TON (dial. people)
- A 35ac: BUFFOON: Wrongly making fun of Abo comic: *(FUN OF ABO)
- N 36ac: ALIST: Stalin perversely belonging to top star group: *(STALIN)
- Y 37ac: ROTOR: Revolving constituent operations research returned Conservative: O(perations) R(esearch) reversed + TORY
- C 38ac: GAEA: Fixed cage about divinity: *(CAGE) + A(bout)
- O 39ac: SEPTUPLET: Group of notes curiously spelt out en passant: *(SPELT OUT E(n) P(assant))
- N 1dn: DAMSEL: Old unmarried woman to censure Scots individual: DAMN (censure) + SEL (Scot. self)
- V 2dn: ECHELON: Mostly authentic half-speed (loosely) pursued by new ranked arrangement of troops: ECH(t) (authentic) + VELO(city) (speed, loosely) + N(ew)
- E 3dn: TERNE: Unchangeable old alloy: Double Definition (ETERNE = unchangeable)
- N 4dn: AS ALSO: Concerning nose bone turned round too: NASAL (concerning nose) + OS (bone) reversed
- I 5dn: NOGAKU: Drama organised in August briefly OK: *(IN AUG OK)
- E 6dn: DRIPFED: Supplied food through tube, irregularly predefined, flustered nurse away: *(PREDEFINED - E(nrolled) N(urse)); isn't it great that there are so many kinds of nurse?
- N 7dn: APPALTI: Italian turns up supporting mate chasing cloth contracts in Rome: NAP (cloth) + PAL (mate) on IT (Italian) reversed
- T 8dn: EXOGEN: Old plant export not originally convincing: EX(port) + (c)OGENT (convincing)
- T 9dn: SIMURGH: Rising fog by old city with bodiless ghoulish monstrous bird: MIST reversed + UR (old city) + G(houlis)H; ref. Simurgh. Has everyone read Worm yet? Budget some spare time, then go read it.
- I 11dn: CON-ROD: Short linking device working within raised type of Greek pillar: ON (working) in DORIC (Greek pillar) reversed
- M 12dn: NONI: Plant found in overblown omnipresence: overblowN OMNIpresence
- E 16dn: ANYHOW: Maltreated husband one way at least: *(H ONE WAY)
- F 18dn: KABAYA: Indeed getting into spirit securing excellent short tunic: AY (indeed) inside KA (spirit) outside FAB (excellent)
- O 22dn: ACT DROP: Advanced mode of cutting including one's own curtain: A(dvanced) + CROP (cutting) around TOD (own)
- R 23dn: CONFORM: Adapt grain species: CORN (grain) + FORM (species)
- A 24dn: INWOVEN: Complicated hotel, hosting without formal greeting: INN (hotel) around WO (without) + AVE (formal greeting)
- N 25dn: RETIAL: Of a network of nerves connected with light sensitive tissue: Double Definition (RETINAL = regarding the retina)
- Y 26dn: TRESSEL: Very French cunning accepting English support: TRES (Fr. very) + SLY (cunning) around E(nglish)
- O 28dn: ARBOUR: Furiously roar about cropped bower of trees: *(ROA(r) ABOU(t))
- F 29dn: PROMPT: Don associated with politician to primarily help with words: PROF (university don) + MP (politician) + T(o)
- T 30dn: LENGTH: Stretch temporarily provided great height: LENT (temporarily provided) + GT (great) + H(eight)
- H 31dn: SHTETL: Jewish village hotel regularly supporting troubled Esth: H(o)T(e)L under *(ESTH)
- E 33dn: OUTS: Excels, abandoning party, reveals sexual orientation: OUTDOES (excels) - DO (party)
- M 34dn: ALEPH: Heartless paragraph at end of masculine letter: P(aragrap)H after MALE (masculine)
So the extra words complete the quotation in 1ac and 22ac, which read (after filling in the blanks) “Death and taxes and childbirth”. The bottom line read PR?M?NTH?H?LL, and after a little bit of meandering – “prom on the hill”? – the obvious “pram in the hall” came to mind, and indeed Connolly is visible down the main diagonal.
That gives me an opportunity to mention (relatively safely, since surely no-one reads these crossword blogs) another aspect of my productivity. Like some, I don't think that a pram in the hall is necessarily the ultimate “sombre enemy of good art”, but I think it is true that having children can change priorities: in BC days, it was perfectly possible and reasonably common for me to stay at work late, or work in the evenings or weekends in addition to a more-than-full working week. This is not to say that this doesn't happen at all any more, but it's certainly much less routine, and to an extent the evening and weekend work is now necessary to get my working time up to a full working week, given the need to do school runs or hospital appointments. And one thing that successful work in academia might share with art is its vulnerability to distraction: in academia, prestige and progression come from high-profile research, which both needs focus and tends to be what is achieved after all the other things have been dealt with: teaching, certainly, and any substantial administrative responsibilities. It's perfectly possible to do useful amounts of administration in the 20-minute block of time when a child is entertaining themselves; deep thought, as with programming “flow”, takes time to achieve.
And maybe the moral is that it comes back: in retrospect, it might not have been sensible to move house, start a company and have a child within the space of one year. I suspect there's no good time to do any of those things, let alone all three, and some of the lack of motivation and energy was down to, well, tiredness: but it feels like I am substantially more productive than I was two years ago, and that is a good feeling.