I think it's simply inner groove damage, which in my experience is much more prevalent on choral, vocal and piano recordings; not just the old mono ones, but also lp's from the late 70's when light tracking force was all the rage. It is not suprising to me at all that an all orchestral piece has none, even if played more. My stereo guru says that people used to align their mono carts at the edge of the record, rather than with the usual null points.
I returned a $300 mono Furtwangler Tristan because of inner groove distortion, even though the records looked perfect. That was uncomfortable. I love mono Classical opera, so I zero in on the very last tube-cut editions, which have that great tube sound. It's your best chance at the least damaged monos, IMHO. Of course, you've got how many stereo releases from '58 to '89 to choose from? : )
I returned a $300 mono Furtwangler Tristan because of inner groove distortion, even though the records looked perfect. That was uncomfortable. I love mono Classical opera, so I zero in on the very last tube-cut editions, which have that great tube sound. It's your best chance at the least damaged monos, IMHO. Of course, you've got how many stereo releases from '58 to '89 to choose from? : )