About the apparent lack of gold gilt (goldplating) on your excavated brass button:
Since your button's backmark doesn't include the word "double" or "triple" (or "treble"), it most probably had only a single layer of gilt plated onto its brass body. Buttons get handled and shoved through the buttonhole every day, year after year. That rubbing action tends to wear away the thin gold plating.
However, some of the goldplating tends to remain in "recessed" areas on the button (such as the valleys in an emblem) where it was somewhat protected from getting rubbed off. Based on my own experience with digging many buttons like yours at early-1800s sites here in Virginia, and cleaning those buttons, there's a decent chance that with some non-abrasive cleaning, the recessed areas on your button's front would still show some gold gilt.
Opinions vary widely on what are the best methods to non-abrasively clean excavated buttons. I myself prefer soaking them briefly in a 50/50 mix of water and ammonia. I put that mixture in a milkjug's cap, and set the button in it for 2 or 3 minutes. Then remove the button, and gently scrub it with the tip of a toothbrush dipped in the ammonia mixture. (Sometimes the button will need a second short soak to reveal all the gold gilt.) Then I rinse the button thoroughly in the sink with running water and the toothbrush. (Don't forget to put the stopper into the sinkdrain first.)
You also asked:
> the RICH ORANGE letters are ever so slightly raised, not indented - does this change the age at all.
Yes. Your single photo of the button's back doesn't make the raised lettering evident to the eye, so I had to assume it was indented lettering. A raised-lettering backmark on a 1-piece brass flatbutton can be as early as the 1790s. But I should mention that the use of raised lettering in backmarks on 1-piece buttons continued for decades afterward. In fact, even some World War One military 1-piece buttons have a raised-lettering backmark.