Due to the read and write offset problems, I discovered some strange results such as zero CRC match in a CD

It seems that the copied CD rip yields junk checksum to the database, right???

Should there be a function of discarding checksum (by manual??) from unwanted CDs and protect the database?

the database is safe. It looks for the identical cd toc and compares the checksums of the ripped tracks. Its only looking for matches, so if there are inaccurate rips it doesnt matter.

Submit your results prior to ripping from CD-R and then delete AccurateRipUpload.bin and the contents of the AccurateRipCache subdirectory immediately after ripping from CD-R. Depending on what program and version you use you'll find them either in the EAC directory or in the C:\Documents and Settings\<User Name>\Application Data\AccurateRip directory.

Eli is right, AR works on positive matches and even takes measures to prevent CD-R rips from appearing in the confirmed section of the database (though there may be preference given to the CD-R rip if it is the first one submitted). Still, I think it's a admirable to want to avoid polluting the database with data that doesn't come from rips of original CDs.