Probably the very first thing that you learn from tv writing books is that you should never spec shows that have already gone off the air. That is because nobody's going to read your outdated spec. Those scripts are goners.
At the same time, it seems that not enough attention is paid to the fact that just because you wrote a script for a show that still exists - a show that might exist for years to come - your script might already be pretty outdated.
But how can it be so? How can it really be a goner? I mean, it's just a spec and a writing sample from me. It's not meant to be sold. It's meant to be read. The show is still on.
The paradox in this whole thing is that even though spec scripts are not meant to be sold or produced, they're still supposed to be relevant and actual. It's much better if your script is up to date within the show's universe.
Every spec script gets outdated at some point - sooner or later - but there's no point in giving it a short life span. At least when you do it on purpose. The longer you can keep it 'alive' and in theory producable, the better.
Serialized tv shows are admittedly the most difficult to spec and die fastest. It's not fun to spec a show like 24 or Lost or Prison Break. There's not much point in writing a stand-alone episode. You have to write an episode that fits within its current season's story arc.
Therefore, "serializing" your script if you don't have to do it, is probably the worst mistake that you can make when it comes to your script's life span. No matter what you do, don't make your script about something that can't happen anymore.
If you want a good (bad) example, let's take a look at a show like Modern Family that gives you plenty of opportunities to keep your spec fresh and alive. It's one of the safer shows out there. (South Park being probably the safest).
Nevertheless, I managed to read a logline for a spec script that read like: "While Gloria is pregnant, Manny and Jay.." & "Now that Haley has moved out..". Lots of restrictions already in the logline for the reader.
Let's be honest here. This script was filmable for like three months at most when it comes to the pregnancy.. and perhaps for like two weeks before Haley was expelled and came back to the Dunphy house.
I don't know about you, but I wouldn't ever do something like this. At least for me it's pretty obvious that the longer I can keep my spec alive, the better. Making it unfilmable right from the start is just...