No, "working" means that they were operational. They existed in the Wii U version of the game in some playable,
working form, with their duo mechanic presumably intact (as Sakurai did not mention any changes). If they existed in the game in some playable form and were working just fine, then it'd take considerably less work to simply polish them up, bugfix, balance, etc. for the Wii U version, than to recreate veteran fighters from the ground up like they did with Lucas, Roy, and Mewtwo.
Also, here's Sakurai's exact words:
Source (Gaming)
"playable during development on the Wii U." They were
playable in their original, duo form. They were fully operational, decently developed, able to be used presumably without any major hiccups. If they were
playable during development, that's a good bit of work done already. It'd take significantly less work to polish an existing veteran character, than to remake one from scratch (which they've done before for DLC).