Tomorrow is today and today is yesterday!

Many of the adults that are rarely referred to on a first-name basis seem to have used multiple names over the years.
Emil Ratburn became Nigel Ratburn by the fifth season, Herb Haney became Francis Haney at some point - and of course Sarah MacGrady became Leah MacGrady by the cancer episode.

It was my impression that "Leah" in the Mystery Envelope episode was supposed to be someone else.

So a while back a user called Earwig posted about an Arthur episode where one drawn character didn't have a head. The idea was someone could send in their own photo to be mapped onto the character. Such a thing never aired on PBS.

I dug it up myself, though I think one of these was posted on here before - oh well. I couldn't believe this was actually made, as opposed to being some benign plan that was shelved before it was developed.
When I grew up watching Arthur, I can't recall seeing this promoted in any form. It obviously dates from Season 5, going from Puberty-Yarmush's voice and the slightly jaundiced animation (a"highlight" of season 5). Apparently it was done for PersonallyYoursBooks.com - they do other jobs similar to what was done for Arthur.

Teaser video: https://www.youtube.com/watch?v=HKBmNf3TLJI
One episode: https://www.youtube.com/watch?v=J3898dPx9g0

When I first saw it, I thought it may be a fake (or one of those wretched but oh-so delightful parodies). But inspection of the specimen has revealed it to be plenty legit - sadly. The photo-mapped head looks very cheesy. It would have been better (though perhaps more expensive) to render the kid as an animal-person the proper way. The name "ANDY" is also badly dubbed in - only two audio bits of "ANDY" are used, and it is tacky.
There are also many songs featured in the one known episode - it's not that great, only Buster's song is passable.

What is shown of another example in the teaser video is no better - only a kid D.W.'s age could think it was such an amazing thing.
The character all seem more gimmicky than usual - I can't exactly put my finger on it, but it goes beyond a typical episode. Maybe it's Arthur's dad's terrifying recipes... he's usually a decent cook.

It was an interesting (not necessarily good) idea, but it's really let down by how cheaply made it is. I don't know how many episodes were done, though I doubt very many were eventually made. The cited website doesn't seem to offer the Arthur DVD anymore, so I presume the offer has been discontinued. Maybe young kids would have liked it, but I think they could have done better.

Oh Tina, Tina, Tiny Tina! Tina Tina Nope. Nuh-uh.

Well we never got to see what "Tiny Tina" was supposed to look like. So I drew up a doodle of what she might look like.
I suppose we'll never see her on the show, as she was only mentioned in Arthur's Perfect Christmas. Nothing ever since then.

Peanuts, by Charles Schulz.

I was almost fooled. For a good few seconds, I had another show in mind. 

I don't really know why I drew this. It's not even that good, though I suppose I nailed Arthur's looks. 

Simply put, this is the product of boredom. Enjoy!

Jenna just couldn't be developed into any character archetype that wasn't already used. We already had the jock (Francine) and the quieter kid (Fern) - Jenna usually fell into both of these archetypes, without much else to offer. Her last role (that I've seen anyways) portrays her in a more kindly light (the nuts episode), but it still offers nothing that more established characters couldn't pull off. I do think after 16+ seasons, Arthur could do with a change-up from the old Arthur gang - but that probably won't happen. The core characters are just too well ground into the show to really retire any of them.

I don't think she's a bad character, even if she was brought up by provocation in her two main episodes ("The Good Sport" and "Jenna's Bedtime Blues").

As for the bedwetting habit, that's fairly low-key in the Arthurverse. Buster is now known to suck his thumb, so what has Jenna got to lose?