MOR,
I believe what The Deil's Child was referring to when he said "posthumous grant" - and he can correct me if I'm wrong - was the grant of arms to "a Scottish ancestor settled in the United States of America prior to 1783" as referred to here.(www.scotarmigers.net/pdfs/info-leaflet-8.pdf)

That leaflet, and a couple of others on the SSA website, offer information - also provided on Lord Lyon's website here http://www.lyon-court.com/lordlyon/f...OfPetition.pdf - on matriculating a grant of arms for oneself once an ancestor's arms have been determined (either by a grant "for and in memory of" said ancestor, or through research to determine the original grant).

It may be that the current Lord Lyon won't grant arms "for and in memory of" long-deceased ancestors. That would be for him to clarify. If so, the information on the various Scottish Arms/Heritage websites will need to be updated.