What is the explanation? If
-regex '^.*[0-9]$' works, shouldn't -name '*[0-9]' have worked in the first place? Don't get me wrong, your code looks fine by itself; but the answer makes an impression that -name is wrong for the job and -regex is right. Why? The OP's code didn't work probably because the files in question were modified on August 7, the question was posted on August 8, so -mtime +6 did not match the files at that time. OTOH your answer was accepted on August 9. There is something fishy here.