23JH could be 23rd March 1933 or 23rd March 1959.
15RL could be 15th November 1937 or 15th November 1963.

You need to look on the label on the back of the packets to see where the ammo was manufactured to know which of the dates above apply to your ammo. Kynoch repeated the year code (the last letter in the code sequence). Details of the powder type shown on the front of the packet also assists in determining the year i.e. cordite or nitrocellulose.

Imperial Chemical Industries (ICI, Witton UK 1926 - 1963

Imperial Metal Industries (IMI), Witton UK 1963 - 1972

If you wish to PM me with your email address I'll send you by return a Kynoch Dating article I have, containing all the code and packet labelling information.