We find out Oliver and Shane's full names: Oliver Joseph Lindley O'Toole and Shane Shannon McInerney.
The entire cast believed the last movie (To the Altar) would be the final movie made and so many of them took home mementos. Kristin Booth took home not only some of her favorite "Shane" clothes and shoes but Shane's necklace as well, the one she wore continuously since the first episode. When Kristin learned they would be shooting another movie she started looking for Shane's necklace... and couldn't find it. Finally she let producers know the necklace was lost so they could order a new one. Then as she was packing to leave to film the new movie she opened up one of the bags with Shane's clothes... and the necklace was at the bottom.
This movie explains what was previously considered a goof in the story line continuity: when did Oliver's mom leave. In the movie Signed, Sealed, Delivered: Truth Be Told (2015) Oliver says his parents divorced when he was 13. Then in the movie Signed, Sealed, Delivered: Lost Without You (2016) Joe tells Oliver about a fight they had when Oliver was 7 or 8 and she left them shortly after it. Most fans thought it was odd that it took 5+ years for them to divorce after she left. In this movie Oliver explains to Shane that his mom left twice. The first time she left she came back after a few months but then a few years later she left them for good.