When is the last time a living current or former president failed to take part in the funeral events of a deceased president?

I tried looking at the last several, to see who participated, according to Wikipedia:

Bush1 (2018) - Carter, Clinton, Bush2, Obama, Trump present
Ford (2006) - Carter, Bush1, Clinton, Bush2 present
Reagan (2004) - Ford, Carter, Bush1, Clinton, Bush2 present
Nixon (1994) - Ford, Carter, Reagan, Bush1, Clinton present

Johnson (1973) - Nixon present

Truman (1972) - Nixon absent, by Nixon's own deliberate choice

Eisenhower (1969) - Nixon, Johnson present

Hoover (1964) - Johnson, Truman, Eisenhower present

Kennedy (1963) - Johnson, Truman, Eisenhower present, Hoover absent due to illness and sent his sons

Roosevelt (1945) - Truman present

By my count, there have been a total of 2 absent current/former presidents over the last 10 presidential deaths. With 29 cases where they did show up. And we're currently on a streak of 20 in a row.

If any living former presidents die before either of these two die, it will be interesting to see if Trump and Biden both show up. If they do, I think that increases the chances that one would appear the funeral of the other.

Some potential reasons a president might not show up, based on this list and some additional brainstorming:

• Personal dislike of the other person (Nixon's absence for Truman's funeral)

• Illness or old age (Hoover's absence for Kennedy's funeral)

• Incarceration (this website thinks there is a chance Donald Trump will be unable to move freely in the future)

There might also be some chance a former president does not get a state funeral, either by his request or due to events during/after their presidency. That could play into it as well.

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Nice question

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