How are double and triple casks whiskies matured?

Question

If a 12 year old single malt Scotch has the label of double cask or double matured (some say double wood), assuming oak and sherry, does it mean

1. a portion of the whisky is matured in oak cask for 12 years, and a portion of the whisky is matured in sherry cask for 12 years and the final product is a mixture of the two in some ratio (e.g. 50:50). OR

2. the whisky in matured in oak cast for some years (say 8) and then the whisky from the oak cask has been transferred to sherry cask for the rest of the years (4) for further maturation.

I hope my question makes sense. Please answer if you know the answer but don't make guesses.

Answer 1

The answer is of course: both

Lets take some popular examples...

Balvenie Double Wood Matured in Ex-Bourbon casks and finished in Ex-Oloroso Sherry Casks, so (2)

Auchentoshan Three Wood Matured in Ex-Bourbon casks for 10 years, then finished for two years in Ex-Oloroso Sherry casks and then finished for six month in Ex-PX Sherry casks, so (2)

Laphroaig Four Oak A vatting of whisky matured in four different types of casks: Ex-Bourbon barrels, Quarter casks, Virgin oak barrels and European oak hogsheads, so (1)