I do have a video on this, but it's not necessary to watch. I am simply passing along this verified information because it's crucial to know and I like you guys n stuff.
There are two versions of MM right now, 2.5 which is Philgo's last version and 3.0 by Sharlikran. Both of these (and ATT) are affected by the throttle in place for data requests from the server. If you use 2.5, you might think /mm missing is solving your data holes but it isn't. Generally, it's timing out after just getting about 10%-15% and just keeps querying the server.
So for both versions of MM, at the present time, the only way you can be sure you are getting all of your data is whenever you log in, go back using guild sales history/e for the amount of hours you were offline.
Further, I checked with Aldanga, who codes ATT, and their answer to my same question was: "ATT still attempts to pull history at regular intervals, but addons are still throttled. If you want all of your data right now (or you won't be or haven't been online for a while), the only way to get it is to manually pull."
So your data in any of these programs may trickle through or eventually be fully pulled, but until/unless ZOS gives us the cache on their end they discussed, the only way to be certain you get your info without gaps is to do the guild history technique.
TL;DR Use the guild history/e thing every time you log in for the time you were offline.
for more discussion, see the comments on ESOUI for Sharlikran's 3.0 version of mm or feel free to ask me questions, if I don't know I'll get you the answer.