I only know this of two Lessons as I have only worked on these two lessons.
The one I'm on now, Living after Midnight. First let me say, I don't have a issue with this lesson. I'm only stating the difference between this lesson and the way the band member plays it. But not just the band member Richie Faulkner, but I see other youtube people also playing very close to what Richie Faulkner is playing. I totally understand there is different ways to play the same song. I'm just curious as to why GT decided to pick this way to do it.
You can look up the lesson Living after Midnight here on GT, mainly referencing the opening riff.
Here is a link to Richie Faulkner playing it. https://www.youtube.com/watch?v=1yK_yxI7AlU&t=51s It starts at time code 25:45
Just an FYI, I like GT, but some times on these older lessons, I'll get stuck on something, ether because I can't see what the other hand is doing or I just can't tell or see exactly how the strumming is going. So I'll look at other sources and see the differences between GT and others.
Right now, the part I'm getting stuck at is Lesson - Living after Midnight, part-Rolling through the Changes. At time marker 2:35.
I'm thinking my issue is a combination of the tone I'm using (maybe to much gain) and I'm just not strumming the notes correctly.
Mark.
To answer the original question GT instructors typically do the best they can with whatever resources are available: live videos or official "canned" videos, authorized notation-tab books, just plain old figuring it out by ear.
On some of the older videos the production wasn't as good without multi-cam angles. This is one reason GT tried to continually reshoot older material with updated production standards when it was possible. Other times there were judgement calls or creative license decisions made by the instructor to get the lesson done in the most effective way possible. For example if there were multiple overlapping guitars in an original recording, but the instructor was trying to make a logical composite path through the song to teach it.
Addressing this specific song lesson, it's an interesting case because I don't think either of them are entirely correct (GT's Douglas or Richie).
If you listen to the original version you'll hear there are 2 guitars. Makes sense as JP was a 2 guitar band. On most of the verse you can clearly hear one guitar emphasizing the upbeats of the E power chord rooted at the 7th fret. This is what Douglas does, but Richie does not.
And you also hear another guitar playing the low E palm muted 1/8th note chugging in between each E power chord. Douglas does not do this, but Richie does.
My best guess is that these parts were split amongst the 2 guitar players in JP. And only one of them is Richie's role when he plays with the band. Douglas might have left this part out thinking the other part was more crucial to the song or prominent in the mix. Obviously I can't answer directly for him, so I don't know for sure.
I'm guessing if this lesson was reshot present day it would contain 2 separate guitar parts. But if you are a single guitarist (alone or in a band) you'll have to make the call as to which part you want to play. You can play either part. Or you could make a kind of combination of the two.
Hope that helps.
