Rear differential plug washer/gaskets

Did my rear differential and transfer case gear oil change today ( need more to do front differential) .
Anyway when doing the rear I the gasket/ washer didn’t come off with the drain or fill plug . It did look like it stayed behind but when I tried to pick at it it wasn’t moving, if indeed that was a washer / gasket..
do those normally stay in place ???
The transfer case the washer came off with the the drain and fill plugs ..
Filled up until oil came out fill plug ..
2015 4wd 6 cylinder

 

I'm pretty sure mine came off with bolts last time I did it....I could be wrong though.

I always put a bit of black permatex gasket maker on the threads when I put mine back in so as long as it's snug I know I won't have to worry regardless.