Where to start?
I begin the quest with AWS D1.1-2008 (it is sitting within arm's reach, so why not?). Read clause 3.9, which leads to Figure 3.11. The title may throw the unwary reader off because the figure is titled "Prequalified Skewed T-joint Details, non tubular". A quick look at sketch "A" indicates the angle between members is more than 60 degree, but less than 135 degrees. I believe the angles of 80 degrees and 100 degrees fall within the range for a fillet weld as described in clause 2.2.5.2. The appropriate text to accompany Figure 3.11 is found in clause 2.3.3. It addresses four conditions, one where the angle between members is less than 80 and or more 100 degrees, one where the angle is between 80 and 60 degrees or where the angle is greater than 100 degrees, one where the angle is between 60 and 30 degrees, and last but not least, where the angle is less than 30 degrees.
I venture to say that most readers would categorize the welds occuring in angles between 80 and 100 degrees as fillet welds in the traditional sense (refer to clause 2.2.5.2). When the angle is less than 80 degree, the text of clause 2.3.3 no longer uses the word fillet weld to describe the weld, it simply refers to the "weld" in the skewed T-joint. Is it a fillet weld if the angle between the members is less than 80 degrees? Since it is not defined as such by by AWS D1.1 I would venture that it is not a fillet weld, but it is still prequalified if the weld meets the conditions and limitations defined by AWS D1.1, clause 3.9.3.
What is the situation when welding to a different code? Good luck with that. I offer no opinion.
Best regards - Al