A - Shows an "antique revival" pattern - popular in the early years of the SSA list, had its low point around the mid-20th century, and has come back stronger than ever before in recorded history.
B - No strong trends, although Barbara and Betty spiked the letter around the 1930s.
C - Once again no strong generational trends.
D - The opposite of "A": A mid-century favorite letter, less popular before and after that time.
E - Similar trajectory to "A" but more popular at its original peak as opposed to its second one.
F - A letter that was more common at the commencement of the SSA-list era but hasn't come back into vogue.
G - More common among Boomers and earlier generations than after; had its low around the time most of today's new parents were born, and is showing signs of coming back.
H - Another "older" letter, with its low point in the 1960s and a lesser return since.
I - Notice how the vowels are showing the classic "100-year revival" pattern, similar to how "A" and "E" have followed.
J - Despite the plethora of Jasons, Jennifers, and Jessicas among today's parents, this letter has been pretty perennial but is now showing signs of falling.
K - A "modern" letter, much more popular from the second half of the 20th century forward than before (although starting to decline).
L - Gradually declined through the 1990s, but is now returning fairly strongly.
M - Another perennial letter, although a little less common now than in the past.
N - Fairly perennial, but more common in recent years (Nancy did most of the mid-century propping for the letter).
O - Same pattern as the other vowels (hence Olivia sneaking in a generation earlier as I described when not many "O" names were popular).
P - Like "D" a letter that peaked mid-century (once again allowing Patricia to show up a generation later when the letter was going out of style).
Q - You'll start to notice that many of the "high Scrabble value" letters were pretty uncommon until recently, and have spiked in the past decade or two.
R - Another "mid-century consonant" now in more of a fashion limbo than at its height.
S - More common among today's living adults than in earlier or later years, but only modestly lower now.
T - A Gen-X favorite letter, at its highest in the 1960s and '70s.
U - Follows the same "vowel pattern" as the more common vowels, apart from the "Unknown" placeholder.
V - Most common in the early years of the 20th century, but on name forums is showing growing approval (and thus a potential for coming back in style in a few years).
W - Like "F" a letter more common with the early years of the stats than later, although William itself did most of that contribution.
X - Same path I cued you in on with Q's entry.
Y - Uncommon at the start of the chart, but among the living generations has had its ups and downs (with a limited set of names though).
Z - Similar to "Q" and "X" but did show some use earlier on the charts.