Coventry was removed from the map in summer 1940, to a certain extent Churchill had been waiting for this to happen (Bletchley Park had thee intercepts)

R.V. Jones in Most Secret War lays out an entirely plausible account of how Coventry happened. It's important to realize that militaries hide data like exact targets behind code names to avoid various sorts of exposure, and these code names are also used on what they consider to be secure channels. Famously the Japanese attack on Midway; as Wikipedia puts it (https://en.wikipedia.org/wiki/Battle_of_Midway#Allied_code-b...):

Admiral Nimitz had one priceless advantage: U.S. cryptanalysts had partially broken the Japanese Navy's JN-25b code. Since the early spring of 1942, the US had been decoding messages stating that there would soon be an operation at objective "AF". It was not known where "AF" was, but Commander Joseph J. Rochefort and his team at Station HYPO were able to confirm that it was Midway; Captain Wilfred Holmes devised a ruse of telling the base at Midway (by secure undersea cable) to broadcast an uncoded radio message stating that Midway's water purification system had broken down. Within 24 hours, the code breakers picked up a Japanese message that "AF was short on water."

Ah, and in 1996 the decrypts were made available; per Wikipedia (https://en.wikipedia.org/wiki/Coventry_Blitz#Coventry_and_Ul...):

Since 1996 the Ultra decrypts for the relevant period have been available in the UK National Archives. Between 07:35 GMT on Sunday 10 November 1940 and 05:00 on Monday 11 November a German signal was deciphered and given the serial number CX/JQ/444, paragraph 4. This message set out code words to be used by aircraft on an operation named "Mondschein Sonate" but did not give Coventry as the target or a date. It did say that transmission of a figure 9 would denote "KORN" and hindsight has recognised this as the code name for Coventry. This was not realised at the time however, even though PAULA had been identified as Paris and LOGE as London. Indeed, the word KORN was used in two reports from an aircraft taking part in a raid on Southampton on 30 November, two weeks after the Coventry Blitz. Another decrypt on 11 November or early on 12 November gave navigational beam settings for Wolverhampton, Birmingham, and Coventry but no dates. There was a hiatus in Ultra decrypts from 01:15 GMT on 13 November until 02:40 on 15 November, by which time the raid was well underway: Churchill could not have received new Ultra intelligence on the afternoon or evening of the attack because there was none to give him. Intelligence from captured airmen and documents did not offer an unambiguous picture either.

Back to you:

As for the Buckingham Palace incident, that was a stray bomb, not one of many aimed at the palace that happened to get through.

Move those goalposts. You flatly said this had not happened. Per this account http://www.westendatwar.org.uk/page_id__39_path__0p2p.aspx, which I'm sure can be verified against more solid sources:

During the Blitz, Buckingham Palace and its grounds were struck on sixteen separate occasions (of which nine were direct hits). The Palace forecourt, inner quadrangle and South and North Wings were all marred by high explosive and delayed-action bombs.

According to it, the famous bombing I mentioned was deliberate targeting during daylight:

A single German raider specifically targeted the Palace with a stick of five high explosive bombs. Two of these hit the inner quadrangle, a third struck the Royal Chapel in the South Wing and the remaining two (one delayed-action) fell on the forecourt and on the roadway between the Palace gates and the Victoria Memorial. The explosions in the quadrangle ruptured a water main and blew out most of the windows on the southern and western sides. The interior of the Royal Chapel was lacerated. Four workers were injured; one later died....