The NORD number is a Naval Ordinance Contract purchase number.
4763 indicates the first contract for these sheaths, which was issued in November of 1943. Approx 592K sheaths. Probably started being delivered a month or so later. When that contract was fulfilled, there were several follow-on contracts, each with its own contract number.
From a post on another forum-
NORD Dollar Value Date of Order Approximate Number
4723 $521,000.00 November 1943 592000
6581 $240,000.00 June 1944 280000
6804 $79,000.00 July 1944 90000
8114 $592,000.00 March 1945 672000
8676 $125,000.00 May 1945 142000
ETA: tried to post in nice, neat little columns, but BF posting software strips out extra spaces and won't allow tabs - 4 columns of data