What is the quality of evidence to support virgin conception when sperm is either deposited on the vulva without penetration, or on clothing adjacent to the vulva.
At least one study reported that a number of women self reported outer-course resulting in conception from a survey of 7870 respondents:
Results 45 women (0.5%) reported at least one virgin pregnancy unrelated to the use of assisted reproductive technology. Although it was rare for dates of sexual initiation and pregnancy consistent with virgin pregnancy to be reported, it was more common among women who signed chastity pledges or whose parents indicated lower levels of communication with their children about sex and birth control.
The study attempted to make it clear as to what the differences between outer-course and inter-course were but it's possible a number of the respondents still answered incorrectly. So we still have to accept that these are unconfirmed reports.
At present there is no controlled experimental evidence to confirm that this can happen, and biologically, it seems highly implausible that this actually does happen. Male fertility is reduced when sperm counts drop below 20 million sperm per ml, and this is when the sperm is introduced into the vagina. A normal ejaculate contains 200 million to a billion sperm. From these only a few reach the egg and then more then one is required to breach the corona radiata to allow a single sperm to fertilise the egg. However, pregnancy can occur even when coitus interruptus is practiced since the pre-ejaculate may contain sperm. So, this suggests that much lower numbers of sperm in the vagina then normally considered necessary can still result in pregnancy.
At present there is no experimental data on the passage of sperm through clothing though one would assume it's possible.
So, in summary, the evidence has not independently verified that outer-course can result in pregnancy, and is an area that requires further investigation.