When a hotfix is provided for an already released version, if the same issue exists in the current development release, it is fixed in that release as well so that the next release from Pega has the issue fixed. This applies to both rules and code hotfixes.
Thus, the issues reported and fixed using hotfixes in 7.1.7, should also be fixed in 7.1.8.
When you run the update (not upgrade) from 7.1.x to a later 7.1 version it will check if there have been changes made after the release date of the product. This happens if a fix was generated around the time of the release of the new version and there wasn't enough time to get it into that version. If any post release hot fixes are detected the update will exit so you can review what changes will need to be redone after the update is done.