mmowkj
its quite a common occurance in charter / come scheduled airlines operating long haul, that once a delay occurs particularly over a weekend that they never catch up until mid week when a break occurs in the flying programme.
On double drop flights some airlines use smaller aircraft to fly the pax say GLA-BFS (outbound pax to SFB) then BFS-GLA (with inbound delayed pax ex SFB) to catch up time. If desperate some airlines will miss out stops and coach the pax, ie. SFB-GLA-MAN aircraft routes SFB-MAN direct
Clearly if an airline has spare aircraft then they may substitute, or hire aircraft in. These days unlikely due cost.
All airlines suffer from these sort of delays i'm afraid
