Involving everyone who shows up to meetings is a great way to move forward and/or trim down attendees. Management who enjoys getting their brain picked or homework assignments are always welcome.

That's presuming a healthy culture. In an unhealthy culture, some people will feel pressure to uphold some comment that someone "senior" made offhand in a meeting several months ago, even if that leader is no longer attending project meetings. The people who report to this leader may otherwise receive blowback if the "decision" their leader made is not being upheld, whether such a leader recalls their several-month-old decision correctly or not, in the case they recall it at all. I have found it frustratingly-more-common-than-I-would-like where people, including leaders, retroactively adjust their past decisions so that they claim "I-told-you-so" and "you-should-have-done-what-I-said".

In response to your comment, yes, I would largely be in favor of moving forward only with whatever is said in the relevant meetings with the given attendees of a meeting. That assumes a reasonably healthy culture where these meetings are scheduled in good faith reasonable times for all relevant stakeholders.