I checked the site and evidently they are all single barrel. It is interesting to note though that the Blanton's site in respect of e.g., the Silver, notes it is bottled at higher alcohol content, and then states it is superior in aroma and taste and is bottled specially for the export market. Also, what I now realise I meant in respect of the barrel-strength version is it is unfiltered. Even cut those bottles (4 or 5 last year I bought in Ontario) seemed somewhat different from Original and the Gold. Anyway while I am curious like anyone about these fine points there is no question all Blanton has a commonality.
I'd guess, in light of all I've read, that when Blanton refers to its Silver as superior it is referring to the effect of less dilution, not better barrels.