We may never know, but lots of people saved their negatives. I just bought over 1000 negatives from an estate that date to around 1900 - 1920...I also just sold on ebay a month or so back about 100 glass plate negatives from the 1890s-1910s. That's not unusual at all. However you're not the only person who believes those inscriptions are in McIntyre's hand...as a non-autograph person I just don't know, and after so many years on this forum all autographs not obtained in person are questionable to me.
