The seasons also follow a developing storyline, for example in Season 4 0+1+3+5+7+9+11 were Ork Underground and 0+2+4+6+8+10+12 were Artefacts. Given the Corp contacts and other contacts for Season 5, my theory is that Season 5 will also be running two storylines, one dealing with Corps getting their hands on intel and/or land rights and one dealing with other things.
Though the CMPs they're currently releasing for non-convention LC games for SR4+SR5 (Sprawl Wilds and Firing Line) are solitary missions, though some do have ties with a few metaplot lines. For example, Carbon Copy is part of the Copycat Killer + Silver Platter (SRM04-05) + Carbon Copy line and features Sybil at its finest, whereas Ashes CMP and Ashes Sprawl Wilds are both part of the Ork Underground storyline.
Let's do a quick analysis of a few random ones.
Brothers United: You are asked for help by a Chicago veteran who wants help investigating the creeps he's getting. You check out a school, figure out who's doing what, figure out who the bad guys are and follow them to their nest, then find out it's an actual nest and end up having to kill bugs and stop a Queen ritual. Afterwards, you can either destroy the artefact they used or sell it to one of the 4 corps.
Manhunt: A former cop was helping a guy investigate strange animal deaths near a farm in the Barrens. They were attacked overnight and now need supplies and backup. The runners go there in a gang convoy and start digging around for intel, then during the night the attack begins. They can figure out what exactly has been going on, or find out partially, and even have the option (though it's not written explicitly what that gives you except notoriety and needs errata) of selling someone out.
Assassin Nation: The party is hired to break into the District Attorney's home and score some info. When they get there, they find the DA and his wife killed and the cops on their way. As they run, they find out they've been framed not only for the murder on the DA and nearly every single Assistant District Attorney (save the one), but also for killing everyone at a meeting from a Pro-Prop23 organization. They can get some hints from one of the news channels or go at it themselves. They find the Johnson but he gets shot up and they have to defend themselves for a short while, then the cops arrive. Tosh takes them in and lets two witnesses confirm they're innocent, then the real plan is exposed and they get to bust the ones responsible and clear their names.