When do band-aids go bad? When does the sticky stuff stop being sticky?

I cut my finger last night while slicing some vegetables for a salad. Silly me.

I went to the medicine cabinet and found two boxes of band-aids. One was purchased in 2005 (maybe 2006) in London, England. The other was from probably 2009 here in the US.

The British ones had lost all of their stickiness and came off my finger in less than a minute. Poor. (I tried 2–3 of them before I gave up)

The American one stuck immediately and (today, the following morning) is still holding fast.

So, my questions:

a) Did the British band-aids fail on account of age? (a couple of years older) or are they less well made?

b) How long should domestic band-aids last before they lose their stickiness?