Tim

Several things come into play. We've all seen trust plates on various freight cars. In that case the bank owned the car. Many new cars from ACF, Pullman Standard, Greenville, etc were financed. Cars built by home road car shops were more typically fully owned by the railroad. The later cars would be depreciated over a 10 to 20 year depreciation schedule. Just like your personal auto, a 10 year old freight car isn't worth what you paid for it. This factors into the overall capital value of the fleet, and would have been used in the ICC Valuation of rolling stock report. Financed cars would also have been depreciated, but probably at a rate that was the same as the finance period. 

It's the accountants telling operations when portions of the fleet are worthless and are at the end of their lives. Afterwhich any serious repairs cause the car to be white lined. 

Mark