Not sure if I am understanding your question completely, but I try.
If you selected a set of PV values, .vtx[] , but they look something like pPlane1.vtx[0:245] and you need to grab one distinct name like pPlane1.vtx[99], this might help.
string $sel[0] = ls -sl
; // this just captures the selected data //
string $expandedSel[0] = filterExpand -ex 1 -sm 31 $sel
; // thsi should expand the list into a new array //
int $val = size $expandedSel
; // this should give the number of entries in the array above //
for ($x=0; $x print $expandedSel[$x]; // this will simply print each entry to the script editor for viewing //
Within the for loop is an opportunity to check for the specific Poly Verticy also.
Hope this helps,
Morris