Sorry, but I can't see MICR toner in use in any large quantity at WTC. I'd like to see some case made that it was.
I managed computer facilities at MHT/Chemical bank for 17 years up to 1993 in back office ops as well as branch and subsidiary ops. I only saw MICR ink in one operation and that was desktop printing. Maybe they went through a couple cartridges a year.
In the last couple years I was the specialist , bank-wide in the technical side of communication to commercial customers (IOW, businesses medium and big and our banking peers). IMO, MICR toner and blank check paper would be a security PITA for the department that used it.