@Anonymous User NOW TV is a mixture of live channels, boxsets and catch-up TV. The catch-up episodes usually leave 30 days after airing, and the boxsets come and go on a regular basis.
The boxsets of S1-4 of The Affair are currently available (either do a search from the homescreen, or you can find them manually by opening the NOW TV app and going to Entertainment > Channels > SKy Atlantic > The Affair).
Only S1 of The Handmaid's Tale is currently on NOW TV because Channel 4 own the first broadcast rights to this and so catch-up for S2 was on All4 not NOW TV. Hopefully they will get the S2 boxset but it's likely to be a while yet before they get the rights.
NOW TV has S1-2 of Unforgotten. For S3 you can watch this free on the ITV Hub app, you'll find it in the My Apps section of the homescreenon your stick (open up the app and go down to the A-Z section, where you'll find it in the U section).
For more info on how content works on NOW TV see the following help page
http://help.nowtv.com/article/Why-can-t-I-find-the-show-I-m-looking-for
