I think the obvious answer to your second question is insufficient torque on the recording turntable.  This happened on many recorded sides, one example that comes to mind is the Weingartner "Les Preludes" by Liszt.  The cutting stylus puts considerable drag on the turntable and that drag increases towards the centre of the disc, dragging the speed down.  If the recording turntable motor is not VERY strong and is unable to maintain the corrrect speed throughout the cut, the resulting slower speed towards the end of the side gradually raises the pitch on playback.  With modern digital workstations, this error is easy to fix, but back in the days of reel to reel tape, trying to rejoin the sides on the aforementioned "Les Preludes" was a nightmare.
db 


    On Friday, November 27, 2015 11:48 AM, Andrew Hallifax <[log in to unmask]> wrote:
 

 Thanks for your contribution Jolyon. I am in fact following all such advice
and practices as you describe. We're working on the presumption that
standard pitch seems to have been adopted in Argentina sometime during the
late 30s. Regardless of how true that is, our presumption is supported by
most other discs in the series produced during the 1950's which render more
or less reliably A442ish at nominal 78rpm. 
However, my question to the list was aimed not so much at resolving the
pitching/speed conundrum per se, but in the hope of discovering whether
anyone might offer an insight into why speeds were inconsistent across the
two sides of discs recorded on the same day and bearing adjacent matrices,
and also, why or how certain recordings of this period change pitch during
the side.