On William Rogers, "... manufacture of the F-S Commando knife began when John Clarke & Sons ... had acquired another knife producer, William Rodgers, in 1870 and continued to make knives under both names. William Rodgers third patterns are available to order to this day. Joseph Rodgers was also involved in F-S production from at least the third pattern onwards. George Ibberson made F-S knives bearing their world famous Stradivarius Violin trademark which they first registered in 1873.
The John Clarke and William Rodgers names form part of The Egginton Group of Companies, ...purchased Pocket Knife manufacturer George Ibberson in 1983 and with it, The Egginton Group of Companies was formed. In 1986, the group was expanded when possibly Sheffield cutlery’s two most famous names, Joseph Rodgers and George Wostenholm were added. Other names from Sheffield cutlery, John Clarke, William Rodgers, Jones & Longbottom, William Walton and Stephenson & Wilson are now also safely held under Egginton’s guardianship."
The third pattern commando knife (concentric ringed alloy cast handles) without casted numbers 1, 2, 3 or 4 on the handle towards the pommel would be post-war.
http://www.gotavapen.se/gota/artiklar/fs/p3/fs_knife_p3.htm
"...The William Rodgers FS sterile (unmarked) all black ‘Official’ Ministry of Defence (MoD) dagger is the only Fairbairn Sykes fighting knife in the world that is supplied under Government contract to the British Ministry of Defence and is listed as an inventory item with the NATO Procurement Division in Luxembourg. MoD specifications state that no issue FS knife shall be stamped with any identification marks. This is confirmed in the manufacturer’s official ‘Letter of Authenticity’ which is supplied with this knife. Amongst other things, it provides the official MoD specs number E/1323E and the NATO stock No. 1095 99 963 2037.
Manufactured in Sheffield, England from traditional ‘hand forged - hand ground’ heat tempered hi-carbon steel. Finely balanced for throwing. Point of balance is approximately 11/32” (within 1/16” either way) from crossguard toward pommel nut. Overall length is 295mm. Ringed cast metal handle with 175mm diamond section double-edged blade. Steel crossguard. Non-reflective matt black oxide finish.
The MoD issue sheath with this knife is made from the very best ‘Bridle Leather’ and the tip is protected by a black painted 20 SWG brass chape."
https://web.archive.org/web/2018021...Yg-Deuq28PuloEhBqTRtJggCLcB/s1600/180BMoD.jpg
It is highly like that you have a commercial version of the MOD commando dagger - the model 180B...
"This is the ‘All Black’ model which, in appearance, looks similar to the MoD issue knife. However, it differs in two ways from the MoD. This knife is not balanced for throwing and it carries the makers name and location stamped on the crossguard."
Imho, it would be virtually impossible to accurately date any of these post war knives....