This is what I get when exporting a 12 page file in 134cvs; there's only a masterpage item with pagenumber.
The y coordinates only match for the first page, then the rectangles don't intersect any more.
Cf. pdflib.cpp l. 2239

pdflib process item: pagename= ownpage=0 pagenr=1 changedMP=0
pdflib process item: x=100 x2=162.5 y=901.89 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=2 changedMP=0
pdflib process item: x=100 x2=162.5 y=1783.78 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=3 changedMP=0
pdflib process item: x=100 x2=162.5 y=2665.67 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=4 changedMP=0
pdflib process item: x=100 x2=162.5 y=3547.56 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=5 changedMP=0
pdflib process item: x=100 x2=162.5 y=4429.45 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=6 changedMP=0
pdflib process item: x=100 x2=162.5 y=5311.34 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=7 changedMP=0
pdflib process item: x=100 x2=162.5 y=6193.23 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=8 changedMP=0
pdflib process item: x=100 x2=162.5 y=7075.12 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=9 changedMP=0
pdflib process item: x=100 x2=162.5 y=7957.01 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=10 changedMP=0
pdflib process item: x=100 x2=162.5 y=8838.9 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1
pdflib process item: pagename= ownpage=0 pagenr=11 changedMP=0
pdflib process item: x=100 x2=162.5 y=9720.79 y2=58.5 w=595.28 w2=123 h1=841.89 h2=140 ilw=1