The card says 'Sheffield blade co. New York, N.Y, (makes me think of Frank Sinatra right away) and then below that 'Blades Scotland' quite confusing. Like most other safety razor blade brands I can not find much info on these, what I can say is that it is made of stainless steel, unlike most vintage blades that are made from carbon steel. This must have been made around the early to mid sixties when stainless steel blades started to replace carbon steel, but still had no coatings of any kind, quite a rare type of blade in 'shave world' in terms of specification. The box is unopened, the card has the outer plastic pulling open at at one corner.
Most vintage blades will not be as good as modern blades, they offer something more important, namely nostalgia and exclusivity, not to mention bragging rights with friends and family! Do keep in mind that razor blades prior to 1960 were mostly carbon steel, and today's blades are mostly stainless steel, stainless is more resistant to corrosion and wear, and lasts much longer. Expect less shaves with your vintage blade and dry it immediately after use to get the maximum amount of uses out of it. They will more than likely not provide the best of shaves, so enjoy the experience for what it is, something your grandpa endured 70 or 80 years back
Note* For obvious reasons vintage razor blades are a lot harder (and more expensive) to find than vintage razors, and such items will come and go on our website, grab more than one pack if you could, one to try out and one for your collection, soon enough they may not be available at all!