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Trains under review, as expected (7,5)

Ross

I believe the answer is:

rolling stock

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'review as expected' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for rolling stock that I've seen before include "Railway vehicles" , "Locomotives and coaches" , "Locomotives, carriages etc" , "Railway wagons" , "Rail vehicles" .)

I've seen this clue in The Guardian.
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