Well....Ive had this one cel of mine for going on 
4 years.  It was in a bag that was completely 
sealed off, no vents at all.  And the lines are 
still in perfect shape.  Im of the opinion that 
ventilating the bags might be a bad idea.  I plan 
on buying new bags for all my cels and not 
cutting them at all.  If it worked for my one 
cel, it should work for the others.  All the cels 
I have that have been venitlated all have some 
damage...and the ones with complete sides of the 
bag cut have realy bad damage.