Sanderson Steel was started in Sheffield, England in 1776 and Sanderson Bros. & Newbold Ltd. purchased a small crucible mill in Syracuse in 1876. Their Crown steel was used for the Pigeon Grade in 1893, A1 in 1894, the No. 3 about 1895, and in 1898 the No. 2. Nitro steel was introduced in 1898 for the No. 3 and Pigeon and later the No. 4 and No. 5; Armor for the 00 in 1898, and Royal in 1898. Sanderson used the brand name "Sanderson Bros. & Co." and was one of 13 companies that formed Crucible Steel Co. in 1901. Halcomb Steel Co. opened in Syracuse in 1904, and L.C. Smith was Chairman of the Board of Directors. Halcomb supplied London steel for 0 grades and Royal steel for the hammer guns starting in 1907. Crucible Steel bought Halcomb in 1911. "Crown" was the brand name of the Crown and Cumberland Steel Co., Allegany County, Maryland but we don't know if that was the source.
The 'Belgium LLH' mark of Laurent Lochet-Habran is frequently found on Fulton, Royal, Armor, London, Crown and even Nitro (on an Eagle Grade) so until we chop up and test each, we'll not know if there is any difference in composition or strength. There can be no doubt that (some if not all pre-WW1) fluid steel 'rough forged tubes' were sourced in Belgium, and Sanderson/Crucible may have only acted as the importers. I recently bought one the last two available copies out there of 4th edition of "Catalogue and Hints on Steel - Halcomb Steel Company" and possibly there will be some hints therein regarding their gun barrel steels.
BTW: There should be a report soon out of Dave Suponski comparing the different Parker fluid steel barrels.