Well, classical releases often tell you very clearly when each track (or at least each work) was recorded. Here, I suspect, each track probably contains parts from both performances. I like the Thursday performance better, but there's that annoying cough in the middle—so I'll grab that part from Saturday…
But yeah, sometimes they don't say.
And I wouldn't object too much to changing day x and day x+2 to days x…x+2, as that's only a 1-day difference. But changing "may 16 and 18, 2004; june 15, 2005" to 2004-05-16 to 2005-06-15 loses a lot of information.
If there's actually enough people (including of course some people to do the coding) that want to improve date support, probably a good idea to put some thought in to it. Dates are... complicated. Especially since MB dates go back fairly far—before the Gregorian calendar. But a lot of that complexity we're probably best off simply declaring we don't care.