Missing texts from online account

I was checking our account online and I noticed that one line has missing text/call records for one number.  My daughter's line shows only half a dozen text messages to/from her boyfriend, out of hundreds in this billing cycle-we have only a few days left in it.  We have unlimited messaging and she is an adult so it doesn't matter cost wise or because she is breaking a rule, but my experience with our cell phones has shown it is a good idea to check up to see what is going on when there is a discrepancy.  We had a change made once to our messaging that was not authorized and I caught it because I checked.  Does anyone have any idea why one number would consistently not show for calls or texts?  He is also with AT&T, if that matters, and both phones are iPhones.