One thing I've always wondered: When the police matched up the DNA from the 2005 Fairfax victim with Morgan Harrington back in 2010, wouldn't they have already found any other DNA matches for crimes that occurred before 2010? I would assume that any rapes or murders with DNA evidence left behind would've automatically matched up in CODIS just like Morgan's did. That is why I don't expect a slew of other cases suddenly matching up to JM via DNA. (Not that he isn't responsible for other missing girls, but maybe they don't have perp DNA to compare for some of the other cases.) If there was a DNA match for any other unsolved cases before 2010, they would already know, right?
Yes - that is correct. When the DNA from the Fairfax case was entered back in 2005, there were no profiles that matched (as far as we know) until the profile from MH's case was entered in 2010 and, again as far as we know, there have been no other matches to that profile since. So if both those profiles belong to JM - those are the ONLY two cases in CODIS now that he matches.
Keep in mind, not all DNA profiles developed from evidence are suitable or appropriate for CODIS - these include mixtures and partial profiles. So a case MAY have a DNA profile from a possible perpetrator but that profile is not able to go into CODIS. It can, however, be manually compared to a suspect profile by a forensic scientist.