Information Request 500 NE 3"

Just picked up 15 of these 500 Nitro Express 3" shells and am looking for information on the age etc. I’d ask for (trade) value, but I’m in Canada so cannot ship to most of you anyway. Headstamp says KYNOCH 500 NITRO, no date or other marks. Copper coated steel projectile.

Forgot to check inside the boxes for date stamps etc. but the outside is stamped 2 R T and has the warning about point of impact on a sticker vs printed on the box.

My understanding:

In WWI, with the sudden appearance of tanks, they converted any heavy caliber sporting gun they could find to armor piercing ammo.

The 500NE would have been fired from side by side guns, regulated to a point of aim for a specific hunting ammo. That would have explained the change in aim indicated on the box.

Comments from those more knowledgeable ?

2 R T should indicate a box filling date of 2 November, 1945. Were Kynoch making “civilian” ammunition this soon after WW2 ?. The next “T” year is 1971 but did not Kynoch cease ammunition manufacture in 1962 ?