You say stuff outside affects plotting, we had a very strict rule the title block was at 0,0 no ifs or buts, also had a move all paperspace so title is 0,0 for those who screwed it up. Plotting using a window option and centre at scale we used this for years 100% success rate. Our dwgs had junk at times next to the title block.
(COMMAND "-PLOT" "Y" "" "dwg to Pdf"
"Iso full bleed A3 (420.00 x 297.00 MM)" "m" "LANDSCAPE" "N" "W" "-6,-6" "807,560" "1=2" "C"
"y" "Designlasercolour.ctb" "Y" "n" "n" "n" pdfName "N" "y"
)