And why?

Where did you see this?
The only Radway Green was here years ago in 900 round cans and was unpainted 62 grain in Brando’s and stripper clips
Very accurate ammo
Should have bought a million rounds

U wot M8

I have a few cans I bought from Weidners in 2006.

720 rounds in each can, with bandoliers and stripper clips. Headstamped '92.

Maybe they are just rounding up. Like that German 56gr ammo...

They may have done what Germany and another country did and add a piece of jacket material over the rear of the bullet, to protect the lead, "for environmental reasons."

The German bullets weigh slightly more due to the lead sealing piece at the rear of the bullet.

I bought some of those cans and stashed them, the bandos alone made it worth it and I wish I had bought more. i'd give a mint for the same stuff in 762 NATO!!

Probably a typo.

I think I have 2 or 3 cans of Radway Green stashed in the shop

OP:
You're assuming that the sticker is correct.......... it may not.
I going with the idea that Radway, just like all the SS109/M855 loaders use the same bullet they always did... there was no change.
You are worrying about Semantics, not what the bullets really are.  

(PS....FYI.... no bullets weigh precisely the same.  And mass produced bullets like the SS109/M855 are pretty bad so the variance will be 1-2 grains.
Making this question moot.  )

You are also assuming the tolerance on the weight of projectiles in military ball ammunition is less than 1 grain.

It is not.

The weight can be as low as 60.3 grains, or as high as 63.3 grains.

Don't have any idea if this has anything to do with it, but the ammo pictured was the same ammo that was surplused in the US 10-15 years ago. Some people had issues with that particular ammo in their AR's. The reasons I read about ...and perhaps the 63 grain bullet had something to do with the fact that that particular ammuntion was produced with the British SA80 weapon system in mind. The SA80 was the issued rifle to British Forces at that time....it still may be but with revisions. The SA80 gas system required a totally different gas impulse than the M16. Perhaps the 63 grain weight had something to do with the SA80 performance. If I recall, AR's with rifle length gas systems were more prone to have issues with RG SS109.
My rifles back in those days were all mid length gassed. I was shooting 14.5 & 16" bbls and my weapons were Colt, Spikes, LMT and RRA...I never had an issue with the Radway. Some people did.
I've got no idea if the 63grain projectile had anything to do with it, but it's not a typo.

I shot a bunch of 91 and 92 dated radway that I got from Century back in the day and it was fantastic in my Colt 1/9. I always thought it was 62 gr , but maybe not. The internet gurus back then claimed it would never shoot well in an AR based system , but it always was great ammo for me.

Sir:
One of the reasons I commented earlier about this discussion being about Semantics is this:
Companies like Radway Green, Lake City etc are using a SS109/M855 bullet.  Those designations (ie SS109) refer to a specified bullet design and manufacture, which among other things is it weighs by spec 61.7grains.
(which is usually listed as 62 grains).  
A 63 grain bullet isn't a SS109 Bullet.  Just like a tracer bullet isn't a SS109 but instead a L110.        
So at some point the markings of the can shown got mixed up, it's one or the other, it can't be both...............
Just like is it a 223 or 5.56 load ......?

But it doesn't matter anyways which is correct, since the variance of the SS109 bullet is easily about 2 grains.  
And no, the company importing this ammo didn't pull all the bullets, sort them by weight and then reseat them.

It's a typo, nothing more.    

Now the issue with the SA80's had nothing to do with the bullet, it was the powder, pressures and the gas system.

Here, from this site in 2006:
https://www.ar15.com/forums/ar-15/Radway_Green_Specifications___Please_pin__then_maybe_less_threads_/16-281487/

They didn't. British 5.56x45 NATO ball ammo from the period was all 62 grain. Typo on the label.

Thanks for the link TGH456E.