You said ...
"But a CDRW cannot be erased, "

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A CD-R can not be erased. (per se)

A CD-RW can be erased which is why it is call read/write.

The technology that is used does this:

A laser beam of light is used to microscopically modify the surface of the disk.

A CD-RW only "scratches" the surface slightly so that the "scratches" (i.e., the data written) can be removed. That is, the "writing process" is reversed.
Now, that exact same area on the disk can be "scratched" (i.e., written to) again.

A CD-R, on the other hand, has the "scratches" (written data) made deep and hard and permanent.

That is why CD-Rs are more reliable than CD-RWs.
The data is "burned" into the disk much deeper and more permanent.

cheers,
dr geep
;=]

Remember ... "With Poser, all things are possible, and poseable!"

cheers,

dr geep ... :o]

edited 10/5/2019