According to Father Tadensz Krusinski, a Polish missionary in Persia from 1704-1729, Shah Abbas established rug factories in Shirvan, Karabagh, Kirman, and other areas of the then Persian controlled Caucasians. Some commercial, some royal.
Read all about it in "Oriental Carpets The Philadelphia Museum of Art". Of course, being a friend of the arts, Abbas installed on staff in these workshops masterweavers from Kirman and Isfahan, etc.
According to Charles Grant Ellis "reciprocally patterned guard stripes scarcely survive among Persian carpets except for the "Polonaise" silk rugs of Isfahan and Kashan." He goes on to say that they occur frequently in Caucasian rugs and E. Turkestan and occasionally in Anotolian rugs.
Although the reciprocating trefoil was used in past times a lot as a symbol of royalty and otherwise, in my meager rug book collection there are not a whole lot of them. Abbas sent his court designers and master weavers to study in both Indian and Italian Royal court workshops. Those were very international times.
So I am suggesting that the Shahshavan weavers who had spent time in court, or had ancestors who did, used this reciprocating boarder to advertise their training. It was something to be proud of. That it became conventionalized into a more geometrical form is common, in my opinion, in weavings back home in the yurt, or village, when things don't work out at court, or court is no more.
I am also suggesting that rugs with more than one of these reciprocating boarders may represent more than one generation of Abbas' court time in their heritage, such as the weaver of the soumak rug in "From the Bosporus to Samarkand Flat Woven Rugs" --plate 22. This rug is labeled "Turkoman". Is it mislabeled? It has "floating bullhorns" in it. These bullhorns look a lot like decapitated elements of Kirman Vase carpet boarders to me. Understandable for a displaced Royal weaver to use. Not that they did not have roots further back, in tribal repertoires.
I understand that the reciprocating boarder extend past the Shashavan, and even beyond early Turkman usage, but in the Caucasians, they may distinguish between the weavings of Shashavan and local traditional weavings. I have read , too, that weavings from the area in question, which were made for home use, by locals, used cotton warps. Sue