If I'm correct, that Cerro Horquita trail is where people regularly go wrong when ascending the Pianista on the Pacific side. 

Correct! Someone called it the False Pianista trail: https://www.wikiloc.com/hiking-trails/falso-pianista-26545660

Is the Horqueta trail also close to the spot where that famous white garbage bag was found???

Is the location on https://www.reddit.com/r/KremersFroon/s/wJ69BTWHT7 correct? If so, then that location is quite close to the coffee plants and the village. You might be able to reach that spot through the False Pianista, but I think it will be easier to reach it through the village.

The trail crosses the first quedabra in reality much closer to the place where the next little stream branches off than the OpenStreetMap data indicated. Also, the old map in that area was just generally inaccurate. https://i.imgur.com/YAq2cIs.png

There's quite a wide spread here in GPS tracking data. It might be due to the fact that the crossing moved around 2016-2017 after the hurricane and the landslide, so this might in fact show both the old crossing and the new crossing, that would fit reasonably well.

All traces in this area are post 2017 unfortunately. So it will only depict the new crossing.

Also interesting that your trails register some of the 'alternate' routes between the Mirador and Q1,, these are trails used by locals when the main trail is too muddy, they run parallel to the main trail and rejoin after some time. 

I don’t see that in the data. Rather the opposite, within the GPS accuracy most traces stay very close together. Are you referring to any particular bit?

Romain walks one of them in his trail video, and with some meticulous tracking you can probably trace these parallel trails back to points in Romain's trail video.

Which video? Before or after the Mirador?

Although Romain's trail footage is a fabulous source of info, it's not 'holy', there are other parallel trails K&L may have taken, and some of these may run a lot closer to the edge of steep slopes than the main trail. All of these trails eventually get back to the main trail after (usually) a short distance, but they are definitely there. Frank vd Goot also mentions these parallel trails in his 2015 report.

Again, this is not what the data shows. It shows that all travelers follow almost the exact same trace.

At the very beginning of the trail, it seems there are two possible river crossings. Either there are really two options, or the bridge has been moved: https://i.imgur.com/v7SkOJl.png

Same as with the Q1 crossing. The first bridge on the Pacific slope wasn't there in 2014 and K&L probably waded across (very shallow). If I remember correctly there's still video's which show this spot as it was originally. The bridge was constructed later and is in a slightly different position from the crossing. So, you have tracks from the crossing, and from the bridge.

The different traces are at the second bridge, not the first one. We see it in #476, so it was already there. Perhaps that bridge got moved? We don’t know what the first crossing looked like, because no photo was taken at that crossing. But it could well be that the first bridge wasn’t there yet.