The period during which the site or structure was constructed, installed or created, namely: Pre-69 (prior to 1869), MR-C (1869 to end 1876), MR-O (1 Jan 1877 to 31 Dec 1922), LMSR ( Jan 1923 to 31 Dec 1947), BR (1 Jan 1948 to 31 Mar 1993), Post-BR (1 Apr 1994 to present), Unknown (not yet been ascertained).
- Pre-69 = Prior to construction work commencing on the Settle-Carlisle line (prior to 1869).
- MR-C = Midland Railway construction phase (1869 to 31st December 1876)
- MR-O = Midland Railway operational phase (1st January 1877 to 31st December 1922)
- LMSR = London Midland Scottish Railway operational phase (1st January 1923 to 31st December 1947)
- BR = British Railways / British Rail operational phase (1st January 1948 to 31st March 1993)
- Post-BR = After British Rail (includes Railtrack and Network Rail operational phases (1st April 1994 to present)
- Unknown = The date / period of construction, installation or creation has not yet been ascertained