Source Lines not copied to tax book , but exists in Corp Book

Hi Team ,

An Asset has been created in CORP and TAX books .

This asset has two source lines.

Both the lines have been considered for the cost in CORP Book , however in Tax book only one source line is considered .

The Asset was created in tax book by mass copy .

My question is -

Is it ok to manually update the Tax book with the correct amount ,

Why only one line got copied to tax book ?

Thanks

Shobha