Weekend Australian, Sunday Times 624

Standard cock-up this week: no clue for 16 down. See below for possibilities. The rest is pretty much the usual fare: bad clue-writing, bad puns, one obsure word, one strange spelling, far too many anagrams and part-anagrams.

Across
1. BAKLAVA. BAK(e) + LAVA.
5. DECIBEL. Bad pun.
9. ROOT OUT. ROO + TOUT.
10. CHIGNON. Anag of G (great) + ON CHIN. Unfair.
11. SILVER MEDALLIST. Anag.
12. HUDSON. Anag (with no indicator).
14 & 20. PRINCESS PARROT. Anag.
17. REEF-KNOT. Sandpiper = Knot.
18. USABLE. U = trendy? Posh maybe, but not trendy.
21. PORTRAIT ARTISTS. POR + two anags of TRAITS.
24. ARAL SEA. Anag.
25. REQUIRE. RE + QUIRE.
26. LIMOSIS. Anag.
27. TREASON. Anag of TEARS + ON (= ahead?)

Down
1. BORTSCH. Anag of BROTH inc CS (gas [rev]). This is more normally BORSCHT -- which would also have worked -- but Chambers allows both, as well as BORSCH.
2. KNOWLEDGE. K (back of booK) + NOW (present) + LEDGE.
3. ADOBE. ADO + BE.
4. ASTHMA. Anag of HAS inc T (time) + MA (scholar).
5. DECODERS. Anag of ODD SECRET (minus the T, its tail).
6. CHITLINGS. CHITS (bills) inc LING (type of fish).
7. BONDI. BOND (Street) + I.
8. LINCTUS. LINCT (sounds like LINKED) + US -- The Australian. As if Dorothy were actually in Oz.
13. OCKERISMS. OC (firsts of Old + Cobber) + anag of SMIRKS around E (English). Don't like the singular in the clue and the plural in the light.
15. EMBASSIES. BASS (perch) + IE (that is) inside EMS (Kraut city).
16. Not clued. ?O?I?A?S generates a few things according to the Mighty Neville. HOLIDAYS is most likely. But there are also: BOLIVARS, MOHICANS and NOMINALS. On the obscure list are: LOGICALS, CONICALS and CORIVALS.
EDIT: The Oz has its usual lame apology this morning (23rd March) following the fabulous Times 24,149 (which, incidentally, contains the name of a living person). "The error was in information supplied and the clue is still unavailable". Then they give the answer: HOLIDAYS -- so a lucky guess in the blog above. Send your complaint to: feedback@theaustralian.com.au. They will take notice and may even reply after about a week.
17. RAPHÆL. RAP (sharp knock) + LEAH (rev.).
19. EASTERN. EASTER + N(ot).
20. See 14.
22. REALM. REAL (actual? -- not for any philosopher I know) + M (1000 for ancient Italians).
23. TOQUE. Anag. The anagind is "jockey" -- bollocks!