Sorry for the delayed response. I wasn't certain about the answer, so I spent a little time digging into this. I read the code for a little while, was expecting to find the code for marking leave time, never found it. Spoke with some people, realized why!
A leave timestamp has never been marked on players leaving the raid or being removed from the raid. It was never needed. The only reason a leave timestamp is marked for users who are offline is because that information is provided directly by the Addon API already. Whereas a person who has left is more complicated. The reason it is not needed is because the only timestamps of attendance that matters are timestamps of bosskills and the characters present. When you extract the Raid Tracker data into Guild Launch, those are the events that get listed out for you and tracked. All the time in between is not relevant to the purpose of the tracker.
As for how you should take this information into your method of tracking raid: Run BWL with it tracking, once BWL is done, click End Raid on the BWL raid, get your MC raid roster together and click New Raid. Then you've cut the two different raid instances into their more granular rosters. This may not line up exactly with how you distribute DKP per raid/boss/event etc, but I imagine it wouldn't be hard to adjust. If you don't want to cut those two raid instances into two different tracked raids, you can still just let it continue tracking and when you import that raid, it should properly exclude characters from bosskills that weren't present.
You asking the question gave me reason to get into it and set up a new dev environment for addons that I'm excited about, so thanks for that!
Thanks for your response, i'm glad that my question had lead to something positive.
Many guild systems are different and from experience, using boss kills as recognition for earning points generally promotes and "anti-progress" mentality. The reason being is that people will earn more from farm runs than they will for progression. The argument could be made that we could also include wipes into the factor, but during Mythic progression, some times you'd need to take 5 to review a log to determine what went wrong and understand what you can change moving forward. Progression runs would only be more valuable than farm runs if you guild just mindlessly bangs their head against the problem until you accidently get it right. It also rewards "bad play" during farm runs. If a guy "blows up" in the raid due to not paying attention, I don't feel they should be rewarded for that. So then it raises the question of accountability which is also not always so clear. It's just a very messy way of dealing with it.
Now this is less the case in Classic, as we all know what to do but there are still intricacies and execution variations so I feel the principle is still the same. The one fact that is universal here is time. In all examples, players are investing time to be at the raid. So it makes sense for this to be the measure of reward.
Fortunately, the website is great for this. I can set an interval and a reward per interval and the website will give everyone their fair score. Unless someone leaves early, which is not tracked. So if I as a raid leader forget to manually remove that person from the periodic attendance, they will be rewarded full attendance regardless of if they earnt it. I'd argue that this is the primary purpose of a tracker, which isn't being achieved.
This situation is exacerbated by the fact that periodic attendance (via time) and boss kills appear to be tracked differently on the website. Via previous support tickets I've ascertained that bosses fights are tracked as you'd expect in order of time of kill. However, periodic attendance is tracked in reverse (so time event 1 would be the end of the raid and not the start as it would be displayed on the website). This makes it even more difficult to see at a glance what/when people are leaving.
Now I mentioned this for people switching to alts, as this becomes extremely obvious when a player earns more points when switching to their alt.
In fairness, I had to check for the "new" and "end" buttons as I hadn't a clue they where there until you mentioned it. I will try them next raid to see if they help and I thank you for bringing that feature to my attention.
But I do feel that the time people leave the raid is an important metric to track.
While we are on the subject of CT raid tracker, is there a way of manually adding items to it? We distribute all our loot at the end of the raid and all loot is carried by a single person until distributed. The issue there is that if we get multiple of the same item, the tracker tracks the item x2. I can reduce the number, or assign all the units to another single person, but I can't separate them to later distribute them to different people. IE make it show on the tracker that person A and person B both now have that item.
Thanks again for your support.
The intent is that attendance being taken per boss kill then assumes any given players attendance. For example, a player is present for a boss kill, then not present on the next boss kill, the time that they left the raid is assumed.
I had not considered the fact that 2 of the same item can drop per night (looking at you Flamewaker Legplates) and how CT Raid Tracker would track that. I need to take a look. A possible immediate work around is to make those edits in process of importing your DKP string after raid.
My guild also picks up all the loot and distributes it at the end. CT Raid Tracker certainly isn't capable of tracking loot trading. This is something I've never found a tenable solution to. The most direct and available work around to this is to edit the "Looter" of each item as you pass out loot at the end of raid. You would do this by going to the raid listing, click View Items, right click on the relevant item and hover over Edit Looter and select the player being given the item. This would then make your exported DKP string accurate when going to put it into the website.