Flagging Interest

Question

^{An entry in Fortnightly Topic Challenge #45: Flags}

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UPDATE: There was an error in the original version in clue 15-down, which has been fixed.

In this cryptic crossword, there is something funny going on with the shaded squares. Lengths are not included with the clues. The final answer, which can be obtained by combining the shaded squares in an appropriate fashion, is the flag of some nation. I hope you enjoy!

ACROSS

6 Patriots' Hall: New England uses first-string in catastrophe
7 A measure of hydrogen atoms containing neutron? They are detected, but don't really exist.
9 Created home for troubled teens, unwanted in the end
10 Waving a noble red flag
11 Holy book's spoken about discord
13 After losing last hata, Abe collects yen for flag
16 Craftsman found in island housing requires roof
18 Within text, Izvestia chief trashing Lenin
21 Single mother heading to gynecologist in northern England to conceive
22 Kansas City markets
25 Twice-yearly harvesting amanatsus, nectarines, neems, uglifruit, apples, melons, climbing citrus fruits
27 Woman in love after an uplifting note
29 Polished cover of their original offering in Paul's latest, Two of Us
30 Someone paid a dollar to hold fourth chair's trumpet

DOWN

1 Fear to erase memory from unit
2 Flag doing strange about-face from updraft
3 Capacity to assimilate central problem of Galois theory
4 Gritty Naples provides home to essential luxury & depravity for one with no inhibitions
5 Bad Moon Rising music, all mixed together
6 Flag enthusiast lets in no one. None.
7 Imitation of atoms in language?
8 She casts her gaze around Spain, in Spain, far south Spain
12 Prepare to turn over last wage for strike
14 Wagon erected to carry one who has departed
15 Skids piss off gathering subway commuters: rights ignored by left [OP: there was originally an error in this clue which has been fixed]
17 Ornate flag on oaken frame
19 Flag after hurting spine skinning elk
20 Heavy metal scumbag on dose of drug between two Molly hits
23 Flag, banner gives heart to peasant
24 Holds firearms up before shooting lead
26 1990s multimedia phenomenon with Moby, Drained and Stone Temple Pilots
28 Splitting last two laps in Bristol, VA NASCAR track

Text Version

Shaded squares are indicated with an asterisk.

-------------------------------------------------------------
|███|███|1  |███|2  |███|3* |███|███|███|4* |███|5  |███|███|
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|6  |   |   |   |   |   |   |███|7* |   |   |   |   |   |9  |
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|   |███|   |███|   |███|   |███|   |███|   |███|   |███|   |
-------------------------------------------------------------
|9  |   |*  |   |   |███|10 |   |   |   |   |   |   |   |   |
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|   |███|███|███|   |███|   |███|   |███|   |███|███|███|   |
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|11 |   |12 |   |   |   |   |███|███|13 |   |   |14 |   |   |
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|   |███|   |███|███|███|   |███|15 |███|   |███|   |███|*  |
-------------------------------------------------------------
|███|16 |   |   |17 |   |   |███|18 |   |   |   |   |   |███|
-------------------------------------------------------------
|19 |███|   |███|   |███|   |███|   |███|███|███|   |███|20 |
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|21 |*  |   |   |   |   |███|███|22 |   |23 |   |   |   |   |
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|   |███|███|███|   |███|24 |███|   |███|   |███|███|███|*  |
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|25 |   |26 |   |   |   |*  |   |   |███|27 |   |28 |   |   |
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|   |███|   |███|   |███|   |███|   |███|   |███|   |███|   |
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|29 |   |   |*  |   |   |   |███|30 |   |   |*  |   |   |   |
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|███|███|   |███|   |███|███|███|   |███|   |███|   |███|███|
-------------------------------------------------------------

Answer 1

The filled grid:

Clue explanations (as best as I could get them; bolded parts either don't seem grammatically correct to me, or I don't understand them.)

The shaded cells

each have two letters: we can interpret these as country codes.

On top are ST (Sao Tome & Principe), SO (Somalia), PH (Phillippines), PA (Panama), and SS (South Sudan).

On the bottom are MA (Morocco), TR (Turkey), NU (Niue), CL (Chile), and DM (Dominica).

To get the final answer,

check the flags of each of these countries. Each one has stars on it!

ST: 2 stars
SO: 1 star
PH: 3 stars
PA: 2 stars
SS: 1 star
MA: 1 star
TR: 1 star
NU: 5 stars
CL: 1 star
DM: 10 stars

Adding these all up gives a total of 27 stars. And the flag of Brazil has exactly 27 stars on it!