I think there is just not a lot of consistency on MDL in general. Look at the Thai BL series, Our Skyy 2. There is a MDL entry for the whole series. There is also an entry for each couple's episodes (two shows each), so there are 8 of those listings. Then there is an entry for a crossover episode, which is the exact same two of the previously mentioned 16 shows.
The whole thing is just completely confusing (and frankly ridiculous) the way it is entered into MDL. It should have been either separate couple episodes (probably not), or just a complete series (probably this). If you didn't want to watch all 16 episodes, then don't watch them, or mark them as watched, or even just ignore them. Either way, there was no need for 10 separate entries for the same show!
Alternatively, these pairs of episodes could have been tacked onto the listing for the original part 1 of the couples series.
I agree with the basic premise in the OP that Western shows don't work the way that shows on MDL do. Even when shows are separated by lengths of time, on different TV networks, have a special nighttime episode, or with different actors (look at soap operas of all 4 of these) they are normally considered the same show and would typically appear in somewhere like IMDB as one show. There are exceptions of course...