An in-show explanation is that Sheldon is a hypochondriac and his afflictions are arbitrary at his whims and desires.
His arbitrary whims and quirks are usually the prime driver of the episodes.
Last night at a get-together, I read your post to a couple of my friends.
“Life was cruel in Virginia City,” is now one of our catch-phrases.
The Chinese have a word for that!
And mother and daughter were buried side by side? Doubly morbid! 
Is that the episode where Oscar and Felix meet briefly in some room as little kids in the 1930s? (I think Oscar’s dad was a bookie, and Felix’s dad was (perhaps) a lawyer?)
However, this wasn’t the Odd Couple continuity error that came to my mind first, but rather the layout of Oscar’s apartment which changed drastically, from a squarer layout based on the movie set in the early episodes (with a hallway that had an iron gate divider), to a more ‘TV filming friendly’ set - the apartment with the low platform area just inside the main apartment entrance (and the set walls angled out, centered on the living room). Checking, I find IMDB agrees with my memory:
"During the first season (1970-71), the show was filmed in the same apartment as the one in the 1968 movie in single camera format with a laugh track. Beginning with the second season, the show was filmed in a studio in three camera format before a live audience. "
Ah, you say, perhaps the in-series explanation was that Oscar and Felix moved to a new apartment over the series - except for one episode where they think the apartment is haunted (IIRC the air conditioner was making odd noises), Felix asks Oscar how he found the apartment in the first place, and Oscar replied he scanned the obituaries to find recently deceased people who had lived in good apartments.
There are a LOT of series with that type of continuity break, though. Happy Days, for one…the Cunningham house early on had the front door on the left. Then they switched to the layout that held for most of the series, with the front door on the right. It should probably also be noted that in that later layout, the front and back doors (the one in the kitchen) are on the same side of the house!
What about the oldest son on My Three Sons who got shunted out after the first season, to be replaced by Ernie?
Same actor, different character.
"MacGyver" Pilot (TV Episode 1985) - IMDb - Pilot Dana Elcar plays Andy Colson.
http://www.imdb.com/title/tt0638745/ - Episode where he plays Peter Thornton for the first time. I don’t remember the series enough to know if they got it right from there.
Yes to Abydos. I assume the writers realized that might be too far?
However, as to the other, IIRC, they do have him translate for a couple of episodes or I thought they at least shorthand his learning to talk the language? But I do know they knowingly dropped it because they wanted to get on with it and not have every new planet require the lines about the language, customs, etc.
It’s not uncommon for actors who have played a small role guesting in a show to do well-enough for them to be brought back to play regulars.
Hill Street Blues killed off Dennis Franz and then brought him back as another cop character, who nobody seemed to recall looking strangely like that corrupt guy who shot himself.
In Tru Calling the central characters had a sister who disappeared half-way through the run and was never referred to again.
In an episode of Welcome Back Kotter, Vinnie Barbarino talked about his brothers and sisters, and mentioned that he shared a bed with his brother. In a later episode, he stated he was an only child.
At least “Leave it to Beaver” explicity had the Cleavers moving to a new house at some point during the series (Wiki states the move from Mapleton Drive to Pine Streetoccured between the second and third series).
I think it coincided with the show’s switching networks (CBS to ABC). Apparently they could no longer film on their original lot for one reason or another.
In a first season Simpsons episode called “Krusty Gets Busted”, Krusty the Clown has been accused of robbing the Quik-E-Mart, and reveals in court that he can’t read or write. However, in the season five episode “Lisa Vs. Malibu Stacy”, Lisa is in a studio getting ready to record sayings for a new “Lisa Lionheart” doll when Krusty bursts in, interrupting the session and reading through a group of notecards with Krusty doll sayings on them. I’ve never verified whether Krusty is revealed to have learned to read between these two episodes, so I’ve wondered if it was a case of continuity error.
Isn’t it just easier to assume he learned how to read?
The sayings were so short and so familiar to Krusty that he could recognize them even though he was functionally illiterate - or alternately, he was still trying to cover up his illiteracy by faking use of the notecards, having actually memorized the half-dozen phrases (that he uses every day), instead.
Didn’t they have him learning to read at one point? I don’t recall a scene or anything, but wasn’t there a quick mention that he’s learning. Maybe I’m just confusing it with the “Give a hoot, read a book” posters.
well thanks a lot, you sure sucked the fun out of that show.
i’m never watching it again*.
- statement only extends until this evening when a syndicated episode is broadcast on a local channel.