Previous versions of VEGAS provide multiple thumbnails for video events. In the latest versions of VEGAS Pro and VEGAS Movie Studio, the default number of thumbnails has been reduced to free up RAM and improve performance.
The default number of thumbnails can, however, be changed:

1. To do this, go to "Options" > "Preferences" > "Video".
2. The option "Thumbnails to show in video events" is set to "Head, Center, Tail" by default. 
3. Change this to "All" if you want all the thumbnails to be displayed.

Keep in mind that this setting uses a lot of memory and can impact preview performance.