I've had a different experience than you have with regards to updates, most of the time I have found candidates just sitting on their hands, thinking there's nothing they can do.
Absolutely agree that an update is not compulsory - and that is why I really believe that outside counsel in this situation is requisite. And above all it must be something NEW or you will really annoy people.
I do feel that if someone's been on the waitlist for 6+ months, if they send *one single well, crafted update communique* and they are accepted the following month that's strong evidence that it worked.
Especially because the percentage of those accepted from the waitlist is extremely small. I don't have any specific information for INSEAD but this offers an idea
https://www.mbadataguru.com/blog/mba/mba-waitlist-acceptance-rate-analysis-2019-data/I believe the level of correlation I've seen shows IF done properly, thoughtfully, professionally - the update letter works.
And while we can't be absolutely sure it was the reason for acceptance, by the same token, one can also not be sure a "frivolous" update was the reason for a ding.
It isn't the only strategy however, it's also a good idea to submit the third letter of recommendation or a letter of support, if it adds value to your overall profile: not repeating things but supplementing things.
This might be better if you don't have anything new to submit or it's been detected that you have a few problems in your application.
https://mbaprepcoach.com _________________