2-2 and a half years?
You were thinking about getting an extra one so you didn't have to get two if one died later? And worried you couldn't match it exactly later?
You can't match exactly now actually. And if you'd bought an extra one 2 1/2 yrs ago, would have been a waste of money because you can buy two modules now for what 1 extra cost then - most likely. Until RAM gets really out-of-date, its cost doesn't go up.
And if your system is 2 1/2 yrs old already, odds are really better that the CPU or motherboard will fail rather than RAM and require ditching all 3 items and replacing with newer - leaving that extra stick of RAM in the box unused.
As said above, after it's lasted one year, chances are it'll never fail.