Show source clip timestamp in frames?

You're welcome, I'm glad my solution worked for you! 🙂

I only ever said use it on one clip, and you can always turn it off and on using the try eyeball.

The Adjustment layer was the first thing I tried as I mentioned, it works but the numbers were wrong when I tried it here. 

This is at the beginning (first frame) of the sequence when I use an Adjustment Layer:

?

Again, no. The post start with this sentence:

"Hmm.  That works, but it's hard to maintain, having to add it to every clip and disable them all each render."

I couldn't get the Adjustment layer to show the right time-code, it was starting on some huge number and I couldn't enter a big enough 'offset' in the effects control to set it to 0 on the first frame. So, Transparent Video instead of and Adjustment later is what I ended up with.

Ah... no. Basically no maintenace at all. 

Right click the project and create a New Item, a transparent video. Put that on it's own track above all the other tracks and stretch it out to cover your entire timeline. Drop a timecode effect on it and set it as it is in my screenshot.

Only one clip to maintain, and you'd have to turn off the track (one-click on the track eyeball) when exporting if you don't want the frame numbers.

I gave it a try, couldn't get it. I tried the timecode effect also on an adjustment layer, that did seem to display frames but the number didn't seem to be relevant to anything? Then black video. That was closer but it covered everything. Finally I put a new layer on above everything else of Transparent Video, and dropped the Timecode effect on it, and it was displaying and acting correctly. It's a work around. You'd need to turn off that track when Outputting, but it seems to work OK.