You're unlikely to find poor-quality transcriptions published simply because transcriptions are done in drafts - much like a painter sketching through a painting.
The accuracy of one person's sketches are of another fully-completed painting - much like an art forger - are either convincing or they're not. The best obviously fool everyone. In order to determine a transcription's accuracy, it would have to be compared to the original score - and even then, the original manuscript (if it still survives.)
Further, there is a matter of notation. If I notate something with quarter notes @ (1/4=) 60bpm, it will sound the same as half notes @ (1/4=) 120bpm. There again, you would have to make a distinction between what is aurally correct is what is notationally correct.
There are composers who have done transcriptions of entire orchestral works. So, the limit of human hearing has not yet been surpassed. Musicians have a keen way of taking very complicated things and breaking them down into manageable bits - no matter how complicated. Your research would have to focus on the amount of material a human being could notate / remember on a single pass through the music.
Certainly, you would also have to separate your data into transcriptions done by people with Absolute Pitch and ones done by people without Absolute Pitch.
As you can see, it is very difficult to answer a question that still needs to be further defined.