Of course simple explanations like we still have to complete bridges, double tracking and ballasting the new tracks along the FECR alignment and testing 110mph operations through zillions of grade crossings and sealed corridor operation is a completely inadequate explanation for a 3 to 6 month push back to inauguration.
Frankly, the early 2023 date came out of the expected completion of construction date for the OIA multimodal station AFAICT. The assumption somehow was that all the complex traack work would be done by then. When we visited the OIA station with the FECRS group they basically said service will start sometime in 2023 without commuting to anything more than that. And this was now many months back.