I have jumped in on this topic before. Our concept of how “accurate” the ORERS misses the point of their intended use and how the railroads maintained the information in them.
They were NOT intended to be a roster of equipment! They were used to describe cars in interchange service. If a car was interchanged, it needed to be included in the ORER data. If a car was listed in the Register but it had already been stricken from the books of the owner IT DID NOT MATTER as that car could not be interchanged. In that case, the quantity of cars in that series would be incorrect. I expect there would be many errors for car series in the process of being scrapped or renumbered. Between the lead time needed to get the data for the next version on the Register, time to print and the time that copy was “current”, scrapping, renumbering or addition of new cars would continue.
Using Southern Railway System data, there are multiple internal memos discussing changes to be made in the next ORER. There are examples where a car series was shown in the ORER that did not exist. In one case, a group of rebuilt 40’ box cars were shown to have 70-T capy, trucks. In anticipation of the cars being placed in service, the ORER listing was modified before publication. Problem was, the cars were rebuilt with 50-T trucks so they could not be used in interchange service with those ORER road numbers.
Again, a Sou Rwy example, when a series of cars was due to be retired, the "quantity of cars” did not need to be maintained exactly. Cars would simply “disappear” from interchange service. Maintaining a “count down” of car quantities in the ORER served no business purpose.
So new cars could be used as soon as they were delivered, the entire series would be listed beforehand. Like scrapped cars, if that road number did not yet exist, there was no way the car could be interchanged so the “error” would be meaningless.
I agree ORERS are important documents but, while railfans may want to know how many cars are in series “X”, that was not the reference used to update ICC records or a railroad’s mechanical data or rosters.