I have a 2400yd spool of Realine that I have been using for years. It has been stored inside away from light probably still 1000 yds on it. How long do you think this is good for.

I'm also a Realine user and have a number of spools left.  Too bad it's not made anymore.

As long as you keep it in a cool, dry place out of the sunlight fishing line should last a long time.  I have no idea what time wise that would be but you'll probably run out of the line before it goes bad.  

spray it with KVD L and L conditioner this stuff is incredible

Just soaked it good last night ready to respool today.

I'm still using mono (Trlene XT) from a bulk spool I got in 1981 or 1982.  Works just fine.  Kept out of the sun and away from heat, mono will last a loooooooong time.

gonna second the whole no sun/heat thing here......ive fished the same spool of ande 10lb mono for about 3yrs and never have a problem...i store it tied in a plastic grocery bag inside of a dark closet.