Pink and grey tab colors in time machine

I have seen explanations saying that the grey colored tabs in time machine are snapshots stored on the local drive and pink snapshots are stored on the external drive. I notice that the grey tabs are not necessarily complete. I was looking at my time cards and I noticed that the pink tabs had my last weeks time card file, but the grey tabs did not. I have pink and grey tabs intermixed running back in time. I am not sure why that is so.

So...

It appears that the grey tabs are generally not complete records. Is that true?