Gatwick - East Croydon is £4.90 Any Permitted SDS, but is down in Brfares as £5.70
Greater Anglia fares are noted as completely wrong by BRfares:
"One or more fares below are set by train operating company GREATER ANGLIA (AGA). Some fares set by AGA in this issue of the National Fares Manual (particularly Super Off-Peak fares) are known to contain errors, such as missing restriction details and incorrect prices. Please check details with a rail booking office if possible."
E.g., it says
"WRE SUP OFFPK DAYTC" Audley End - London Terminals £19.20, valid weekends only (code FA)/
But the correct fare is £21.50, and the validity is D6, which I can't find, but it appears to be valid 7 days a week, albeit obviously with time restrictions.