Im not sure if this helps but did a similar trip over 4 months from the start of March to the end of June in 2018 from CBR also all in J!
Can confirm backtracking was allowed.
CBR-SIN-LHR,EDI-IST-JFK-BOG-LIM-SJO-CUN,LAX-HND-ICN-SYD.
backtracking from LHR-EDI, EDI-IST. ICN-SYD is technically...