I just received the answer by Musicvideo10 on the Sony forum side.

It sounds like you're already quite familiar with this but it's all I could think of for now. Make sure you added the plug-in as a Track FX if you want it to display for the entire timeline, otherwise, if you added it as an Event FX it will only display during the playback of a particular clip.

For Vegas 12 Pro it's: Tools, Video, Video Track FX, then select the Sony Timecode plug-in.

From the Sony Vegas Knowledgebase:

https://www.custcenter.com/app/answers/detail/a_id/1113/kw/timecode/session/L3RpbWUvMTM2NzUwOTY4Mi9zaWQvUnd4SmJicGw%3D

Thanks, Mark. It was the split screen icon -- I had it inadvertently turned on (never use it).