Disi, I have seen both Avg. and VG used to refer to a stamp on which the perfs cut into the design. FWIW, both PSE and PF use VG, as noted in their respective guides.
http://www.psestamp.com/pdf/2009_Gr...e_092009.pdfhttp://www.philatelicfoundation.org...-booklet.pdfAs far as the stamps in the 2c block are concerned, I think your grades are on the high side.
The UL stamp is noticeably off-center towards the bottom, which I believe makes it F-VF, even though the other three sides are almost perfectly even.
The UR stamp has perfs touching or slightly cutting into the frame at the lower left, which puts it in Avg/VG territory (F at best).
I'd call the LL stamp VF, but not XF, because of the difference in the top and bottom margins.
And I think the LR stamp is F because the perfs on the left are very close, and it also has a noticeably narrower margin on the bottom than the top.