Rear tang thumb safety switch attachment

Putting back together my trigger assembly on action after bedding my new stock and have encountered a puzzler.
I am dumbfounded on how the sliding thumb switch attaches to the safety tab that sticks up through the slot in the tang. When I removed, I thought the thumb switch had a grove underneath that locked onto the safety tab to keep it tight but that doesn't appear to be the case.
I figured there would be a video or some instructions on the net to explain but I struck out.
The top of the safety tab that sticks up through the tang has grooves cut into it, so I thought maybe glued, but no evidence of that.
I'll probably have a doh moment once explained, but I am buffaloed.

the button will slide back and forth... come right off without the piece that slides along on the underside and protrudes up into it. When all is assembled, it holds together fine.

First put the top/thumb button in place, then the sliding bar underneath.

Once the triger assembly is installed and the pins inserted, it will hold together.

I am not the sharpest knife in the drawer, but that is what I have done a couple of times. As I am inserting the spring and working the pin through the trigger, the thumb switch just wants to drop to the floor. When I dry fit it unassembled, it tends to slightly lock in place, but still has a tendency to separate if I pull it straight apart. I'm feeling like an idiot.

The thumb piece has a groove it slides into...

the sliding piece on the underside has a part in the front that sticks up into the action and the other end has a part that sticks up and into the bottom of the sliding thumb part. You gotta position the thumb part just right so the underside part will slip into the underside of the thumb part...

remove the thumb part... look at the inderside of it... there is a square recess that accepts the square "peg" on the rear of the underside piece...

you gotta slide the thumb part into the rear of the tang and be sure it glides in its track well. then move it towards the rear, I think, and insert that square peg into the underside of the thumb part in it's square recess. the thumb slide has to be in just the right position forward and back... push it back and forth till you can get the square peg into it... It's that sliding bar (underside part) that keeps the thumb piece from sliding too far back on the tang and coming off.

Sorry, i don't know how to do pics.

Thanks Foxx, for your patience and info. I could see all of the details you outlined, but still was baffled. Today, I took it back apart, laid the thumb switch on top and brought the bottom piece up at an angle(everything toward the rear) and after a couple of tries, it finally held. You were right about it had to be just a certain way. What an odd mechanism, but it seemed to work. Now I will be paranoid about the thumb slide falling off since it is attached ever so slightly.

Don't be. :) Once it is assembled, it can't come apart. The sliding bar on the underside is trapped between the trigger assembly and the action.

But, yes, when the trigger assembly is removed, it can all fall to pieces. But it's fine. Trust me. :)