I believe the Laker One-Eleven services to the Canaries were indeed on the edge of performance, but they used a range of techniques to be inside the regulations, starting with only allowing an even less baggage allowance than the normal IT 15 kg. Did they do refiling of flight plan destination at the halfway point, as they passed Oporto ?
Laker had been a first user of the more capable One Eleven 300, which had more power and lifted more fuel, but broke the US weight limit for two-crew operation there, which the original 200 series aircraft had been sized to fit, The series 400 then had all these new features, but a lesser "paper" MTOW to suit the USA, commonly by not having full tanks, which the US operators did not need, and did not have the maximum passengers IT cabin layout. Their One-Eleven operations would have been the first nonstops to the Canaries by an aircraft without an FE - doubtless hence the comments !