The article mentions "an example of 彁 mistakenly used in a digitized Taisho newspaper due to a faded printing of 彊", but to me that implies the symbol already existed before then.

Isn't that backwards? The nonexistent character is in the -digitized- version so presumably OCR or something got 彊 wrong, that's not saying that 彁 was used in the -print- version.

Indeed, the source link is about exactly this: a crappy scan appears to have 彁 but a better copy reveals it was 彊.