German to English Tech/Engineering Mechanics / Mech Engineering Engineering drawings - Title block

All,

I am translating engineering drawings for communication equipment. Shown are components of handsets, cradles, etc. All components are injection moulded from plastic.
The drawings are from Germany, drawn in the 1980ies and have fairly standard title blocks following DIN 6771.
There are two abbreviations of fields on the title block that I do not know what they stand for:
One of them is “P-Nr.”
The two fields are located in the very bottom left corner below the “Maßstab” field.
Other adjacent fields are: and “PT-Nr.”, “Benennung”, “Zeichnung Nr.”, “Ersatz für”, “Ersetzt durch”.

Target language is English US.

Any help will be greatly appreciated.

Peter