I learned a valuable lesson this week.

A few months ago, I stumbled upon a pre-release notification for ‘Eight is Enough.’ It was only $15 for the first season and I remembered the show fondly – so I ordered it.

Tuesday, the show arrived on my doorstep (thank you Amazon for always being prompt). I popped it in after work that night, preparing to laugh at the fashion but relish the show.

Boy was I wrong.

The pilot episode had not one, not two, but three different kids in primary roles – Adam, Tommy and Nancy respectively. Now, I had known about the David recast – Mark Hamill (Luke Skywalker for the great unwashed) had to leave the show for a little film series called ‘Star Wars.’

I didn’t remember the other recasts, though.

Now, it was a pilot, and it’s not like this is the first show to ever do some recasting after the pilot was already shot. Anyone remember the other D.J. on ‘Roseanne’? How about the other Sookie on ‘Gilmore Girls’? Or (shudder) the other Willow on ‘Buffy the Vampire Slayer’? No, you don’t remember them.

That’s not the only problem with ‘Eight is Enough,’ though.

Even though it was a big story at the time, here’s a quick refresher for those not up on their 1970s celebrity scoop. Diana Hyland – the mom, Joan Bradford, on ‘Eight is Enough’ – became ill with breast cancer four episodes into the first season. She died (in boyfriend John Travolta’s arms) before the show ever made it to the air.

While I understand that show runners weren’t sure if Hyland would be able to return to production, the fact that Joan Bradford’s absence was never addressed was a huge lapse in continuity. It didn’t help that the episodes were clearly not shown in the order they were filmed.

In one episode, daughter Nancy is freaking out because Joan stole a job that she wanted. In the next, there is no mention of Joan and husband Tom Bradford is complaining about doing all the laundry for the kids. Then, in the very next episode Joan is back and planning a party for family friends. The episode after that? You guess it, Joan is missing again and there’s no reason given.

Since Hyland’s health was so precarious at the time, why didn’t the writers have Joan go visit a sister out of town? Or how about leaving to take care of sick parents? This would have explained Joan’s absence without treating the audience like idiots who didn’t know she was missing.

That got me to thinking, though. There are a lot of 1970s shows that are considered classics but wouldn’t hold up today because of continuity issues.

Let’s face it, in this world of Internet message boards the continuity police would have doomed our favorite childhood shows before they ever made it to air.

Take ‘Little House on the Prairie,’ for example. I loved the show as a kid (and I still watch it as an adult). However, there are huge continuity issues.

Take the character of Albert, for example. In one episode we’re told he returns to Walnut Grove to be a doctor in the future. A few episodes later he is killed off. A few episodes after that Walnut Grove is blown up (mostly because Michael Landon had a fit that the show was cancelled, but I digress).

That’s just one example. Quite frankly, instances of botched continuity number in the hundreds on ‘Little House on the Prairie.” It doesn’t stop me from enjoying the show – but I don’t hold it up as some paragon of greatness like I do other shows.

There are times I don’t think that the attention given to certain shows by some fan bases (read: nonstop whiners) is good. I’m guilty of it, too, though. In the last season of ‘Buffy the Vampire Slayer,’ one of my biggest quibbles with the season has to do with a continuity mistake. In that one, teenage sister Dawn (who thinks she is a potential slayer) says that her sister would have to die for her to get the job.

Whoops. Not the case. It is established in season three that the slayer line no longer runs through Buffy. It runs through rogue slayer Faith. A little thing, I know, but it was enough to send me into a tizzy.

On the flip side, the CW’s ‘Charmed’ was also a genre show that had constant lapses in continuity – but that fan base didn’t seem to mind. Of course, the quality of that show was much lower than the quality of Buffy.

Then you have high concept shows like ‘Lost,’ ‘The Walking Dead,’ ‘Game of Thrones,’ and ‘Battlestar Galactica.’ Those shows are really built on continuity – so much so that if even one question isn’t answered, fans revolt.

Take the original ‘Star Trek.’ That show had gaffes and writing omissions all over the place – including the fact that Spock and Kirk would go on every away mission together. Cut to ‘Star Trek: The Next Generation’ decades later.  That show wasn’t perfect, but the changes in continuity were enough to flabbergast viewers – many of whom cite the second show as the greatest ‘Star Trek’ franchise (yours truly included, too).

So, what am I saying?

It’s not like I’m going to give up on the older shows I loved as a child. I still put in ‘The Incredible Hulk’ on rainy weekends when I have a lot of cleaning to do – for example. When I watch that show I try to ignore how ludicrous it is to believe that Bill Bixby’s pants could fit on Lou Ferrigno – or how he never seemed to be traveling in a straight line – I just love the show for what it was – campy fun.

The same goes for ‘Little House on the Prairie.’'

For some reason, though, ‘Eight is Enough’ does not fall into that category for me. I’ll be unloading that DVD as soon as possible.

Maybe some shows are better left as warm memories than disappointing realities?

What do you think? What 1970’s shows hold up and which ones don’t?