They haven't even been NOTES since Series 1963, when they removed the words "will pay to the bearer on demand". They are now IOU-nothings.
Before Series 1963, it also used to say "This note is legal tender for all debts public and private, AND is redeemable in Lawful Money at the United States Treasury, or at any Federal Reserve bank."
So not only was it not "Lawful Money" (or money at all, but a promise to redeem it on demand for Lawful Money. Removing these promises did not magically transform the pieces of paper into "Dollars".