Bear with me, and if I'm wrong, then I apologize up front!

You said, a butterfly and a stamp, when a single butterfly stamp is all that is needed for a 1 oz. letter, that requires the NON MACHINEABLE surcharge.

A butterfly stamp includes the cost of a 1 oz, letter rate (78 cents), and the NON MACHINEABLE surcharge (49 cents), at $1.27 for the single butterfly stamp.

However, a butterfly stamp is not required to pay the NON MACHINEABLE surcharge. Regular stamps, in a combination of $1.27, along with the envelope being marked (typically in red ink) at the bottom, left-hand side of the front of the envelope, in block lettering, "NON MACHINEABLE", will also work, as will a Forever stamp (78 cents) and a combination of regular postage stamps, totaling 49 cents, and the marking, will also work.

Lastly, if an envelope requiring the NON MACHINEABLE surcharge is also a 2 oz letter, an additional amount of regular stamps, totaling 29 cents, must be applied, but not a 2nd application of the NON MACHINEABLE surcharge is not applicable.

I frequently mail single and 2 chips with the single butterfly stamp, and 3 chips with a single butterfly stamp and 29 cents more for the 2nd oz. But never for chips worth more than a few dollars, each.

Shown here are 2 versions of the NON MACHINEABLE butterfly stamps from the USPS and 1 example of the 29-cent, 2nd-ounce surcharge rate. All 3 are also Forever stamps.