In general, when a hotfix is issued for 7.1.6 (or any other version), the fix is put by Pega in both 7.1.6 and whatever version we are currently developing.
So, if we're developing 7.2, and during that development a hotfix is issued for 7.1.6, the fix is put into 7.2 as well.
The danger is if a hotfix is issued for 7.1.6 after 7.2 is released but before 7.3 is released (assuming 7.3 is being developed. I can't say it is. We might be developing 7.2.1 or decide on some other name). In that case, the fix goes into 7.1.6 and 7.3, so if you update to 7.2 after installing the hotfix in 7.1.6, you'll lose the fix.