I'm not sure what blight or what article you are referring to. Lilacs get a number of diseases, which vary from nuisance to deadly. So you should be certain of your diagnosis. Without photos, I can't help.  Here are a couple of diagnostic sites:
https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/lilac/
https://yardandgarden.extension.iastate.edu/article/2021/08/summer-foliar-lilac-diseases

And here is a link to the plant disease clinic:
https://pdc.umn.edu/submit-sample

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The fungus looks like lichen, which I would expect to see on a 100 year old lilac.  Sorry, but the "blight" I can't identify.  There are a lot of lilacs suffering from the excessive moisture this year and there are a number of diseases.  The only way to tell what yours has so you can treat it properly is a lab test. I suggest you send a sample to the plant disease clinic (link in my first post). The disease might be pseudocercospora (which is mentioned in one of the links in my first post):
https://yardandgarden.extension.iastate.edu/encyclopedia/lilac-pseudocercospora-leaf-spot

If you want to avoid the lab test, then clean up fallen leaves and wait and see.

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