‘One for all’ standardized land pattern v.s. specified land pattern in datasheet
The correct footprint to use for a component land is 'one that works'.

This isn't so flip as it sounds. 

What does a land pattern have to do in order to 'work'?

a) it must connect each component leg to its pad
b) it must not connect it to adjacent pads
c) it must pull the component into correct alignment when the solder is liquid
d) it must be visually inspectable 

These taken together mean the lands must be at least as big as the lead, but not too close together. There is considerable latitude in how much bigger the lands can be. It's this wide latitude that allows there to be multiple designs.

A land that is much bigger will satisfy (a) and (d), but might get solder stuck between the lands so fall foul of (b).

Whether a particular footprint is solderable without getting connectivity between lands depends to a large extent on the process the board assembler uses, and to some extent on the thermal capacity and lead positioning accuracy of the component. If different manufacturers use different assembler processes to refine the footprint, it's not surprising that they might end up with slightly different pad sizes.

What is surprising is that the process works as well and as often as it does.

A case in point. I was once using a 0402 packaged diode, and the manufacturer was aiming it towards very small, so very high packing density, boards. As a result, they specified a land pattern that had copper areas exactly the same size as the component pads. This resulted in a small solder volume with no side or toe fillets, that our particular in-house reflow process often failed to assemble properly. I had to fight our reactionary production manager and his 'always use the manufacturers recommendation' footprint policy to use lands that were larger and more suited to our solder process. Once we had more solder, and fillets, the yield went back to 100%. It's likely that were we using a thicker solderpaste stencil it would have soldered OK, but that would have been inappropriate for our other components with their more generous lands.