You may have conducted the same quick search and found the same info. Of course, they didn't change a lot of stuff on these so it's quite possible that the same model was sold from the late 50's to the late 60's.
Columbia's were one of the better quality bikes in its day, on par with Schwinn.
I'm curious, what is the serial number? It should start with a T, e.g. TS09049. If you have a good serial number your best bet would be to contact Columbia Bicycles. I would note that a lot of folks have had very similar year/model tandems (perhaps even this one) and have struggled with getting an exact dating, even after giving the serial number to Columbia.
Whoops. My bad. That's where it should have been. All of Columbia's bikes have the Serial Number stamped near the rear drop outs. Colson had them on the bottom brackets.
The number -- as I suspected -- doesn't appear on most Columbia SN tables. You can contact Columbia's Customer Service folks and ask them if they can peg the production year but I'm not sure if even their records are complete with regard to the tandems.
As you can see, no mention of T (which must = tandem since it appears in front of all of the tandem serial numbers) which suggests a different number system was used, e.g., the one I mentioned above is a TS....
If I was a betting man, I'd "guess" the period of manufacture as '63 to '65, assuming the second digit was an "O" and not a "Zero", but that's really a WAG.
Let us know what, if anything, Columbia can share regarding tandem Serial Numbers.