#2957: A Crossword Puzzle explain

[A square 15x15 crossword puzzle is shown. Only 21 of the 225 squares are black. The black squares are in a pattern that are 180 degree rotationally symmetrical. Three black squares down from the 11th column and similarly three black squares up from the 5th column. Three black squares out from the right in row 7 and then two more black squares diagonally up from the end. Similarly three black squares out from the left in row 9 with two more black squares diagonally down from the end. A single black square is three above the first black square on the diagonal going down to the right and similarly there is a black square three under the first of the diagonal squares going down to the left. (Row 6 column 12 and Row 10 column 4). Finally there are three black squares on a diagonal crossing over the central point by going up from the left through the central point (Row 8 column 8). There are numbers at the top of every column (except the one that is a black square) and similarly at the left edge of all rows (except the one that is a black square). There are also numbers at the bottom of every black segment (except the one that reaches the bottom) and all rows after black segments except the one that reaches the right edge. In total all numbers from 1 to 51 are written. They are written in reading order from 1 to 51.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

[Below the square there are two columns of clues for each number that belongs to across (rows) and to the right there is one column of clues for each number that belongs to down (columns). Both segments have an underlined and bold title above the clues. ]

Across

Famous Pvt. Wilhelm quote
IPv6 address record
“CIPHERTEXT” decrypted with Vigenère key “CIPHERTEXT”
8mm diameter battery
“Warthog” attack aircraft
Every third letter in the word for “inability to visualize”
An acrostic hidden on the first page of the dictionary
Default paper size in Europe
First four unary strings
Lysine codon
40 CFR Part 63 subpart concerning asphalt pollution
Top bond credit rating
Audi coupe
A pair of small remote batteries, when inserted
Unofficial Howard Dean slogan
A 4.0 report card
The “Harlem Globetrotters of baseball” (vowels only)
2018 Kiefer song
Top Minor League tier
Reply elicited by a dentist
ANAA’s airport
Macaulay Culkin’s review of aftershave
Marketing agency trade grp.
Soaring climax of Linda Eder’s Man of La Mancha
Military flight community org.
Iconic line from Tarzan
Every** o**ther letter of Jimmy Wales’s birth state
Warthog’s postscript after “They call me mister pig!”
Message to Elsa in Frozen 2
Lola, when betting it all on Black 20 in Run Lola Run

Down

Game featuring “a reckless disregard for gravity”
1010101010101010101010102→16
Google phone released July ‘22
It’s five times better than that other steak sauce
ToHex(43690)
Freddie Mercury lyric from Under Pressure
Full-size Audi luxury sedan
Fast path through a multiple choice marketing survey
12356631 in base 26
Viral Jimmy Barnes chorus
Ruby Rhod catchphrase
badbeef + 9efcebbb
In Wet Leg’s Ur Mum, what the singer has been practicing
Refrain from Nora Reed bot
Mario button presses to ascend Minas Tirith’s walls
Vermont historic route north from Bennington
High-budget video game
Unorthodox Tic-Tac-Toe win
String whose SHA-256 hash ends “…689510285e212385”
Arnold’s remark to the Predator
The vowels in the fire salamander’s binomial name
Janet Leigh Psycho line
Seven 440Hz pulses
Audi luxury sports sedan
A half-dozen eggs with reasonably firm yolks
2-2-2-2-2-2 on a multitap phone keypad
.- .- .- .- .- .-
Rating for China’s best tourist attractions
Standard drumstick size
“The rain/in Spain/falls main-/ly on the plain” rhyme scheme