We maintain a record of all of the ICAR registered tags that we ship and can trace tag numbers back to the purchaser. Our policy is to notify the tag's owner and allow them to contact the finder. We do not give out ownership information without permission.
Another possibility is the so-called "ghost" tag. These are tag numbers that appear once for one scan and are never seen again. They are usually in a number range that has never been assigned to a tag. They are often marked as "W" tags (writeable) and they are always a single scan detection, not multiple ones in a row.
Ghost detections are caused by noise that can generate the correct bit pattern to pass the verification process, a mathematical function called a cyclic redundancy check (CRC 16). The CRC is calculated for the 64 bits of information received from the tag. Normally the CRC check prevents noise from masquerading as a tag but once in a while the noise makes a lucky guess.
Send suspected ghost tag detection records to Oregon RFID tech support if you have any questions.