I have read the article and played with your test scripts and it makes sense. We do not do diffs so it will not affect us now but good to know for future use.

Although I did not know that it is possible to do COPY_ONLY Log backups as well.

I did a test on this and it is possible to delete a log backup from the sequence of backups (if that log was backed up with COPY_ONLY) and not fail the restore -- it just skips on to the next one in sequence.

I then thought, well why not do all log backups using COPY_ONLY and then never have to worry about a lost or corrupt backup again!!!

I assume this text from MSDN answers that question:

"When used with BACKUP LOG, the COPY_ONLY option creates a copy-only log backup,which does not truncate the transaction log. The copy-only log backup has no effect on the log chain, and other log backups behave as if the copy-only backup does not exist."