Great info. I think that may be it
I have a guess what it is - the HMV that is inherent in some Indica landrace strains.
Which is somehow different than your run of the mill TMV - it appears that some Indicas are immune to it and have rendered it relatively harmless even though they still carry it in their genes.
If you read up on TMV - it is highly contagious, fast acting, and can live on dried material for 50 years or more.
If every curved, mosaic patterned leaf was in fact TMV; no one who had one would have a grow left.
I have only heard of one case where a guy had TMV and it wiped out everything several times over for him.
Not that there are many more - just that most mottled leaves are not necessarily TMV as we know it.
Like I said - my guess is the mottleing we have seen recently is benign transfer from breeding.