This has come up a couple of times over in the Sinatra threads. Early Reprise titles were manufactured by Pye Records in the UK, and I'm curious about runout into. From 2010, regarding The Concert Sinatra album: From 2016: From earlier today, regarding a copy of Sinatra Sings Great Songs from Great Britain belonging to @Pieter Kozak : Anybody know about Pye runout inscriptions of the time? Thanks.
The M and WMH suffixes seem to indicate the cutting engineer. I'm not aware as to who these individuals were - the codes of Pye engineers I do recognise point to later engineers. If there's a symbol immediately before this code, such as a star or triangle, it indicates the cutting lathe used. Z/T is the tax code. It indicates the amount of Purchase Tax levied at manufacture, and in this case points to manufacture being between April and November 1962. If the Purchase Tax rate changed between the record's pressing and it leaving the factory, the manufacturer had to apply a stamp to the record bearing the new code. For more info see here: purchasetax
Unfortunately it doesn't help with the Sinatra records but here is a great site for UK matrix numbers & etchings.