It's not "inconclusive" and "there was no reliable evidence" that are different, it's the promoting part that makes them completely different.
"We found no reliable evidence that abstinence prevents teen pregnancy"
"We examined whether promoting abstinence prevents teen pregnancy and the results were inconclusive"
The first is obviously wrong, and if the the second is true it would mean the government should look for other ways to prevent teen pregnancy, but it wouldn't mean that practicing abstinence as an individual doesn't work to prevent pregnancy.
"We found no reliable evidence that abstinence prevents teen pregnancy"
"We examined whether promoting abstinence prevents teen pregnancy and the results were inconclusive"
The first is obviously wrong, and if the the second is true it would mean the government should look for other ways to prevent teen pregnancy, but it wouldn't mean that practicing abstinence as an individual doesn't work to prevent pregnancy.