Finally an answer from Balvenie.
"Dear Mr XXXXX
Apologies if you did not receive our response previously. We did reply to you, but sometimes our emails do not get through. We hope that this one gets through to you.
In answer to your question, The Balvenie RumWood 14 year old is another limited edition matured in traditional oak, then finished for up to 18 months in oak casks previously used to mature Rum. The Balvenie RumCask 16 year old is also matured in the same way (first in traditional oak and then in rum casks for a second maturation period) but for two additional years, giving it an added intensity and sweetness.
We hope this answers your question and wish you many years of continued pleasure in the company of The Balvenie.
Kindest regards,
Online Editor
The Balvenie single malt Scotch whisky"