Kevin
After asking you to post some pics, I am not much help. Hopefully some of the more knowledgeable members can post here. Here is what I found, but nothing that will help with dating the knife. I believe Mr. Thornal passed away a year or so ago, so don't know if the store is still "Randall dealer."
"Andy Thornal is a world class, sporting and outfitter's store, in Winter Haven, Florida and has been a RANDALL dealer since 1969.
There was a time when the sheaths for all Randalls sold at the Andy Thornal store had the Thornal logo above the Randall logo on the back of the sheath. This is not the case today and exactly when this stopped is not known for sure but probably in the early 1980s."
Thornal had three specials. Below is what I have copied from an old thread.
"Their SERIES #1 knife would remind you of a 5 inch blade Model 12-6 Little Bear Bowie with a deep thumb notch in front of the hilt. The series started in 1974 and only 100 knives were made. Each knife had stag handles, the blade was 1/4" stock and the back of each knife was marked A.T.-S, with the serial # under this mark. The last ones were sold in 1985 for $175.00. The back of the sheath is marked ANDY THORNAL SPECIAL above the regular Randall mark. A floral design is present below the stone pocket on the front of the sheath. The sheaths were made by Johnson.
Their SERIES #2 knife is very similar to a Model 5-4" Randall. This 1/4 inch stock blade is 4 inches long and has a thumb notch. The handle is stag with a brass single hilt. The spacers are unusual in that there are only three with two black with one white spacer in the middle. The first knives in this series had sheaths with the floral design also, but later on the floral design was discontinued. Also the ANDY THORNAL mark is on the back of sheath. This knife was first brought out in 1977 and only a total of 100 were made. The last ones were sold in 1990 for $280.00. The back of each blade is marked A.T.-S II # (serial number). The serial # is beside the A.T.-S II.
Their SERIES #3 knife is a Model 26 Pathfinder with a Model 25 handle which was made in honor of their 50th Anniversary. 150 knives were made in this series in the 1995 and 1996. Same numbering system as before. The issue price was $495."