According the the 'lecture' notes, CD-ROM drives have error-correction codes that enable them to read CDs with a black dot marked or a scratch on the surface, provided that their sizes are supported within the specifications.

pictures courtesy of http://www.burn-proof.com/

If you can see from the pictures above, the drive read the CD with the defects with 168 error correction reads for the black dot and 110 error corrections for the scratch. That means that even if the CD may be scratched or even dotted, the drive can still read the disc without any error but just a little delay! 

Have you also ever wondered why while some of your CDs look like they have scratches all over but you are still able to read them without any problem? Well, maybe now you know why. These tiny scratches are known as 'Natural Gaps'.

pictures courtesy of http://www.burn-proof.com/

As you can see, the gap is only a mere 26 microns wide, which is much, much smaller than the black dot or the scratch above. Naturally, this CD can be read by any CD-ROM without any problem at all. And it only took 47 error-correction reads.

But what about BURN-Proof gaps? Take a look at the pictures below.

pictures courtesy of http://www.burn-proof.com/

From the graph, we can see that the gap is even smaller than the natural gap resulting in only 34 error-correction reads! Therefore, one should not worry about the small gap caused by how BURN-Proof works. However, the current generation of the BURN-Proof technology is able to achieve zero gaps, meaning almost no gaps at all. But zero gaps or not, there will always be a theoretical gap.

However, users should not worry too much about these BURN-Proof gaps. To end uses, it's basically invisible to the naked eye, being smaller than 26 microns. So far, I've not encountered any read errors caused by these gaps. I've already explained in full length why this is so. And with each newer generation of the BURN-Proof mechanism, you can expect the gaps to get even smaller. So, there really is no need for any concern over this issue.