Profile for Moritat

I have acquired a large # of Playbills from around 1976 thru 1984. I would like to sell some of them on Ebay, but there is one issue. Although most of them are very clean (near mint condition), the person that owned these wrote a small date with pen in the very top right hand corner (in the white area just above the "LL" of Playbill). On some there is also a name or two. I know this writing will hurt the value, but I'm wondering how much?  Are these now worthless because of

Recently I came into 100-200 Playbills from the 1970s and 1980s. Most are in solid near mint condition with one little issue. Whoever owned these wrote in ink (at the very top of each issue) the date in this format (4/78). The writing is very small and its in the upper right corner, but it does deface these otherwise near perfect copies. How much would this writing bring down the value of these Playbills? I'm concerned that this might make them almost worthless, but I'm not