Doesn't matter at this point as long as you are happy with them. They would be way out of warranty anyway. As for the rattle in some, it has to be loose epoxy in the shaft. If you can turn them upside down and feel like the pieces are in the shaft, just pull the grips and dump out any loose pieces. If that does not work, have the heads pulled, cleaned, and re-shafted at a golf shop. It would probably be good to have them check the lofts and lies as forged irons that might have had a rough life before you could be a little off the specks. Enjoy.

Being as they are over 15 years young, as Dale said, counterfeit is not likely. Most counterfeits reveal themselves in short order. Besides loft/lie adjustments you can have the shafts pulled and re-glued while getting regripped. If you love them, worth the refurbishment. You may even want to use a different shaft if the current isn’t the best fit for you. .

My guess is these are original oem irons.
I played the 680 mb for a very long time and these were a top performer irons.
I made a very bad move when I sold them.
Why I think these are original, is the font stamped on irons are perfect, exactly the one used by oem, this serie was not produced at large quantities like the 690mb. This club was a niche club with the center of gravity placed higher permitting a lower flight.
I do not remember if at that time the 6 iron had a serial number.
If they feel great when strike, it should be oem.

Davis Love111, Adam Scott (for a very long period) were playing these clubs.