One thing I would like to easily find is clear info about time period. I know about (and look for) the build date on freight cars, but can't always see them on mfrs pictures, and there often isn't that info about structures.
That's not that easy. You pretty much have to do your own research if it's important to you.
For example, a car or locomotive might be a design that was first introduced in say 1970 and was in production for a decade.
Road name/paint scheme A offered by the manufacturer is an original as-built paint scheme from 1970 that had untouched examples last up until the modern day.
Road name/paint scheme B is a similar car that was built several years later in 1980.
Road name/paint scheme C is a 1970 built car, but it's a later 1990 re-paint scheme.
Road name/paint scheme D is a 1970 original, but the entire series of cars only lasted five years before being renumbered or sold off to another railroad.
etc.
So out of the examples above, one is pretty much good for about 1970-2010 (forty-year service life for cars built before July 1974; 50 years after July 1974), one is good 1980-present, one 1990-2010, and one only 1970-75. All the exact same car, just different decorations.
The manufacturer uses one standardized packaging for all the cars in this run and there's only so much room to print all kinds of stuff on the sticker label on the box end that identifies which specific paint scheme is in that box.
For structures, unless it's a specific model of a specific structure from a specific town with a known construction date, designs are fairly generic and could have been built any time within a date range of decades. And older buildings from many decades ago still stand today.