I think search of message body text has been a bit flaky for some time. I did recently see some conversation between developers who seemed to have identified why this was and it looked like there was a fix coming along soon. Having said that, many search engines treat numbers as being a bit special and it may not "get" your pattern when it includes numerals. Just to show how contrary it is, some users have reported setting up searches like yours and then being shown matches against the content of images. It seems amazing that a word search would look into the contents of attachments, particularly when it is quite manifest that they are images and so wouldn't contain any readable text.