MTOW variation:
Two ways - structural, or paperwork.
The earliest Britannia 737-200 variant had an MTOW of 49442kg, the final batch 55111kg. They were all designated B737-204 (which was only a customer identifier) but were structurally different - stronger spars at least, maybe different gauge skins, perhaps different wheelbrakes (memory has faded on the detail!)
Later, with the B757 fleet, all the -204 were delivered with the same MTOW. I think this was 113398kg, but all were downgraded on paper to 112699, and later some to 103699kg.
Why do that? To save money. In the 1990s, 3 roughly equal items made up 75% of the DOC, namely fuel, en route charges, and landing and handling costs. The other 25% covered purchase, maintenance, insurance, and crew costs, plus overheads. By reducing the declared MTOW, the aircraft moved into a lower weight category and the airline paid less for en route and landing charges. The savings were significant.
The airline could do this without penalty provided that the declared MTOW was adequate for the planned sectors. As the B757 had more than enough range for all the normal Europe/Med destinations, that was OK, until............
We also went as far as Banjul; easy if the MTOW was 112699, but not at 103699. Of course, occasionally the wrong aircraft was allocated through force of circumstances, and a tech stop would be needed in the Canaries both ways - thus negating the savings........
It just shows that Sod's Law will get you whenever it can