My understanding is that the recent "Welsh tartans" were purposely designed to have different warps and woofs in order to differentiate them as "Welsh tartans" from the typical existing tartans where warp and woof are the same. I suspect it was purely a marketing gimmick, but the effect is often aesthetically pleasing, as evidenced by many of the kilts pictured on this board. I don't know whether this makes them tartans or not- at some point the definition of a "correct, proper, or real" tartan is more aptly described as a "traditional" tartan, where warp and woof are the same, not withstanding assymmetric or non-reversing tartans such as the Hunting Stewart, Old Macmillan, etc.

Cordially,
David