"Don't ask how I know this." I am far too polite to ask that. (Was anyone injured?)
Excellent post. I hope your readers pay strict attention to the modifier/qualifiers, such as "postwar." They can make all the difference.
There are really four issues here:'
1. At some point, ages ago, Lionel decided to make the U post the neutral (return, common, black, or whatever one wants to call it) on transformers that were designed to power multiple loops of track where one could easily operate more than one train at a time. Among these was the postwar ZW. The U posts were generally supposed to be connected to the outside rail.
However, on transformers that were intended to power only a single loop of of track and run only one train at a time, such as the popular 1033, the U post was customarily connected to the center rail. The instructions gave the operator the option of selecting from several choices what post he wanted to connect to the outside rail. A chart of these combinations is available in the "Library" at the Olsen's Toy Train website under the generic heading "Transformers." In some cases, the pages that list transformers by model number add a bit.
2. For reasons that few can recall today, Lionel sometimes violated it's own rules and manufactured items that were quite puzzling -- in whole or in part. One example concerns the whistle rectifiers. It didn't matter much at the time, because neither the whistle nor the horn cared which wire was hooked to what. With the introduction of bells and other sound effects, how things were hooked-up suddenly made a whole lot of difference.
3. In some instances Lionel mixed- or messed-up the instructions such that they failed to clarify the above.
4. This is not ancient history: the early CW80's, which can still be found for sale "new in the box," suffer from all three of the the above problems.
Hope this puts a slightly different slant on the problem.