I'm not sure I understand your question entirely.
The IgM test itself is unreliable, and shouldn't be performed on adults, ever. It doesn't matter if they're type specific or not.
The CDC's 2015 STD Treatment Guidelines - https://www.cdc.gov/std/tg2015/herpes.htm
"IgM testing for HSV 1 or HSV-2 is not useful, because IgM tests are not type-specific and might be positive during recurrent genital or oral episodes of herpes (337)."
http://www.ashasexualhealth.org/stdsstis/herpes/herpes-testing/ - this lists several reasons why the IgM isn't reliable for herpes diagnoses.
https://www.statnews.com/2017/01/26/flawed-herpes-testing-leads-to-false-positives/ - excellent article about IgM testing
https://westoverheights.com/herpes/the-updated-herpes-handbook/ - this is written by Terri Warren, one of the world's leading experts in herpes.
"IgM (a different kind of antibody) tests do not accurately distinguish between the types of virus nor can they accurately tell a new infection from an old one. IgM tests also may pick up other herpes viruses, like chicken pox or mono virus. IgM tests for herpes should be avoided completely until better ones are available. Many clinicians don’t realize that the IgM test is not good for diagnosing people, and tell people, based on an IgM test, that they have herpes. And not only that, they tell them have new herpes infection because IgM, with other viruses, comes up early in infection. But with herpes, IgG and IgM come up around the same time. The IgM can be generated years after first infection and will be detectable periodically. There are also commonly false positives on the IgM test. A person might have an IgM test and four months later, still be IgG negative. The IgG is the only test you ever want for herpes, never ever IgM." - pg 11
We also have several recent threads about people who've tested positive on the IgM. Here are a couple:
So I'm not sure if I answered your question, because it seems as if you want information about the IgM being reliable, but it isn't.