Here's a little more about Signatory Vintage, and why your Signatory Ardmore expression seemed different than the official Ardmore bottling you buy at the store.
As was stated, Signatory Vintage is an independent bottler. There are many independent bottlers. SV, however, is one of the few that is not owned by a larger company and/or distillery. Another is Gordon & Macphail.
These companies (the good ones) play an incredibly important role in the industry. To some extent they are preservers of history. They are the only way to taste an examine closed/mothballed distilleries. Whether they bought a spirit at cask fill, as with G&M, or scooped some up in acquired casks before a distillery was closed and its stock **** off to the blenders. There is also a market for buying casks that were a blenders stock they've determined they're long on.
Additionally, because the independent bottlers stocks of any one distillery are tiny compared to the distillery's stock,they are not blending 100 or more casks at a time to achieve a "profile" of what they want their 10 or 12 year to be. Thus, you are getting a marriage of 3-5 casks, and often single cask, bottlings from the likes of SV, G&M, Duncan Taylor, Cadenheads... So, you're seeing the spirit in a more pure expression compared to most distillery's official bottlings.
Cask selection is also more important. In G&M's case, they're having casks built to their specifications, used by a particular sherry or bourbon producer, and then filled by a particular distiller's spirit for which they originally had the cask designed. Most distilleries aren't this concerned about the quality of the cask, but are more concerned with quantity of casks so as not to short their production.
Further, many of the independent bottlers are filling bottles without chill-filtration and/or addition of caramel coloring. So, you're again seeing a more pure reflection of the spirit than you are in official bottlings. ABV may also be higher.
It's not that all distillery bottlings are bad, but you do improve your chance of having something truly remarkable by incorporating the acquisition of independent bottlings into your purchasing and drinking repertoire. In fact, I buy and drink about 75% independent bottlings. The trouble is finding them because most stores don't carry any!
Finishing on SV, they've moved their offices from Edinburgh to Pitlochry (and their stocks). They function out of Edradour now. In 2011, they completed new dunnage warehouses on site at Edradour for the SV side of the business. They also have their own bottling line at Edradour, so they're in about as much control of their business from still to bottling as anyone (and more so than many distillers!).