We also have our ears. Let's listen to the Soundhouse Tapes.
Listen to the solos in Invasion:
That first solo (my right audio channel) does not sound like Dave. Not in the least.
4:57
The second solo (left audio solo) is clearly Dave.
5:21
The third solo is the "other guy" again:
6:42
The opening riff in Prowler (again right audio channel) really doesn't sound like how Dave would play rhythm guitar either. That goes for everything you hear on that same right audio channel. I feel sure it's again "the other guy".
In Strange World it looks like the channels are switched. The right channel is clearly Dave. The first solo is his, and so do we recognize lots of his playing style that landed on the debut album version.
The left channel features playing that is distinct from what we hear at the debut album version. Also the 2nd solo is different from Dave's style. So I tend to believe this is "the other guy" as well.
Now, even though I can't prove there are 2 different guitar players, I am absolutely not going to rule it out either. On the contrary: it is very likely we're hearing two different guys here.