Aragorn243 If you have an ED51 stamping. The other stampings will be RSAF Enfield Lock inspection stamps. Just for interest I was at the open day at Enfield Island Village last summer
( that is what the Enfield Lock factory site is called now). The bayonet factory is now apartments.

X was the old flex test stamping, but I have never seen it on a No9. I thought the last use was on the 1907 and P13 bayonets. If you have two Crows feet , heel to heel ><. This was the old strike off charge stamp.

I have just cleaned the grease of my mint ED-54 No9 Mk1. Stampings on the side are ED/137 (ED over 137) followed by a broad arrow/crows foot. Blade is broad arrow. Where the blade joins the socket ,stamping is 89 or 68 depends which way you hold it! Stamping on push button is Small crows foot,ED 87. I got this bayonet from Arundle, who had some unissued No4 rifles re imported from the USAicon. It might be from the cancelled Irish Army contract.

Kind regards, Lester