The CHARM discography lists the Brahms Violin Concerto recording with
Szigeti included in the eBay CD link below as a 1959 Mercury recording. Are
you familiar with it enough, or can you access other information about it,
to say whether or not it is in fact an authentic MLP recording? If it is, I
am really puzzled why it would not have been selected by Philips (i.e.,
your mother) for an MLP CD production.