GGG: Is there a 13th stone in WD Gann's Gravestone Geometry?

As I was inspecting the Great Tree with my back to the WD Gann diamond (see HERE), I sensed and saw a large stone perhaps 3 or 4 feet from the trunk of the tree.  This stone, I believe, may have been aligned with stones 12, 10 and 7.  I also imperfectly recall the stone had a round medallion and perhaps it was the stone medallion that had spelled "Endowed" with a four digit number on it.  I know that there was a stone with the word "Endowed" on it but upon inspection of every photo I took that day the medallion's I found only stones numbered 2 and 4 had "Perpetual care" medallions on them.

Is that stone closest the base of the tree the 13th stone?  We have the riddle of the 13th tribe and the many speculations.  Perhaps the intent of the GGG is to symbolically pose the same question?

Consider the triple triangle formed of stones 1, 5, 7 and 11 (green, blue and yellow vectors):

Stones 10 and 12, at the periphery of the formation are not integral to it.  That seems very awkward.  It just doesn't seem correct.  And stones 7, 10 and 12 are perfectly aligned in a diagonal fashion.  I specifically checked that and took a picture to show that alignment:

12, 10 and 7 were in perfect diagonal alignment as I stood behind #12.  If only I had looked behind me about 15 feet or so where, specially, the 13th stone would have been located.  I believe it is the stone I saw next to the trunk of the tree and which, in my best recollection (which might not be good), is the stone with an endowment medallion.

So what would a greater triangle look like with a 13th stone?  I draw it by extending the two vectors formed by stones 5 and 11 and stones 7, 10 and 12 (the light blue vectors):

Their intersection would be where I expect the 13th stone, if it exists, will be situated.  Obviously, it would complete a far more understandable greater triangle when you connect stone 1 with the speculated 13th stone.  I believe the existence of the stone and an endowment agreement may hold key insights into documenting the WD Gann Gravestone Geometry.

So, not having considered the 13th stone question on either of my first two visits, I am destined to make another trip; a third trip.  I must have confirmation one way or the other.

From my home in Virginia Beach, 6.5 hours (theoretically 6 hrs 3 min without traffic, 6 hrs 45 min with traffic per below) to Green-Wood Cemetery and 6.5 hours return home (per Google)…..13 hours of travel.

An interesting take on America as the 13th tribe might be found HERE.  And then you might consider Mr. Gann's emphatic admonition at the top of the 130th page (err, 13X10) of "The Tunnel Thru the Air":

Jim Ross