1) I checked out the page source to try and find a copyright date, but the source is blinded so no luck there. They're both under the new documentation rather than the old, probably updated around the same time. What discrepancies to do you see that are throwing you off?
2) I'm guessing the RecipientId is used for other calls. Much like if you want to export a survey's responses, you have to create the export file (one API call), use the exportId to check the percentage of export completion (another call), and finally pass the [surveyId and] exportId to actually view/download the result set. Your get your exportId back from the first call and use it in the next two.
3) You'd have to burn a Qualtrics account to get a true sandbox.... You can get an API key easily by logging into an account, top-right corner click your icon and choose Account Settings, 4th tab 'Qualtrics IDs', right-side API section, click 'Generate Token'. Pair this with the account email and you're good to go.

Hope I was able to shed some light on these for you!