Your little doodad isn't showing(no not that one) the one above "All else is in doubt, so this is the truth I cling to. " in your sig, just the little square placeholder thingy.

Or, maybe they did!
 
Nah.

Did a little digging. Chances are that while Mr. Welk may not have known the meaning of 'toke' there were certainly others who did. This show was aired at a time when the networks were looking to improve the reach of the show in the ratings and we pushing to add more modern country and pop songs to the show's repertoire.
 
It was also the same time as the Nixon administration, specifically Vice President Agnew came out and labelled the song (among others) as having a profoundly negative effect on America's youth and songs like it should be banded from the radio. The FCC went so far as to put out a listing of banned songs and 'one toke' was on that list.
 
Two good articles we found on the subject are "One Toke on Lawrence Welk" from the Brewer and Shipley web site (http://www.brewerandshipley.com/misc/OneTokeWelk.htm) and "One Toke Over the Line meets Lawrence Welk again ... 45 Years Later" from the The Vinyl Dialogs Blog (http://vinyldialogues.com/VinylDialoguesBlog/one-toke-over-the-line-meets-the-lawrence-welk-show-again-45-years-later).
 
In the second article it states that Gail Farrell is creating a one-woman show in which she answers the question of how much they knew at the time:
"Oh, and as for the question of what Gail knew and when she knew it about “One Toke Over the Line” in 1971, well . . . we still don’t know for sure. They talked a lot about the whole thing at dinner, but neither Brewer nor Shipley directly asked Gail the question, at least not that I witnessed. I guess we’re all just going to have to go see her one-woman show next year for the answer.

Can't square a circle.

A lot of Americans were singing this song in the early 80s, having no idea what "turning Japanese" meant in the UK.
 

'Turning Japanese' doesn't mean anything in the UK.  The guy who wrote that song says he used it as a metaphor for going crazy.

Live and learn. My roommate from Germany misled me. Of course, I'm easily misled. 

This explain why you always saw Myron Floren walking around with a bag of tater chips.

I showed this to my wife a few years back. We both had a good laugh, having both been brought up watching Lawrence Welk (Best thing going in those days). I like Myron Floren's intro "...one of the newer songs.".
Welk was actually quite innovative; in the early TV broadcasts, they tried panning the TV sound all to one side, and you were supposed to tune your radio to a certain station which was panned to the other side, and Voila...Stereo! Didn't work all that well, I guess, and they gave it up.