Literally blown away, Jane.
“ir- serves to intensify,” —
I’ve read very convincing arguments that explain certain double negatives as emphatic negation, which intensify the meaning, as in you ain’t seen nothin’ yet.
But, doing an emphatic negation, with the use of a prefix, within a single word? That’s wild.
The article you link to is fascinating too: irregardless “in widespread and near-constant use since 1795”, and first appeared in Merriam-Webster in 1934.