You are correct.
The 450NE (also known as the 450 3-1/4" Nitro Express) is generally accepted as the first dangerous game nitro cartridge.
It was a development of the John Rigby firm as a nitro version of the popular 450 3-1/4" black powder express cartridge.
They are the same case but the nitro version is strengthened at the base, or web.
The 450bpe had a little brother, the 450/400 3-1/4"BPE which was a 450 necked down to .400.

You can imagine the danger in producing new high power nitro express ammunition that fits perfectly into the chambers of existing black powder proved, lightweight rifles so W.J. Jeffery came up with the 450/400 3" cartridge.
This cartridge has a much thicker rim so chambering it in existing 450/400BPE would be largely impossible. That was a built in safety margin but it is also more efficient as a full nitro cartridge as the neck on the 3-1/4" version is unnecessarily long for a nitro cartridge.
Both nitro versions (3" Jeffery and 3-1/4") ended up being offered with very much the same loading and performance.