parent page or spread?

I'm fiddeling around with this one and i beg for some help:

set currSelection to object reference of item 1 of selection --Script will only be used when text is marked

set parentTextFrame to item 1 of (parent text frames of currSelection)

set parentPage to parent page of parentTextFrame --Get the page

set theLine to make graphic line at parentPage with properties {geometric bounds:{A, B, C, D}, stroke color:"Linecolor", stroke weight:1}

This works fine. But only if the textbox is on a page. But often I prepare those textboxes left/right offpage on the spread for late usage – then the script doesn' work, because parent page returns nothing, and i cant just exchange that with parent spread. I dont't know how to draw the line there. Further I don't know, if a spread belongs to/has a page number: My document has more than one pages, and the line should be drawed over that marked text on the spread.

Can someone help me out?