After The End, frames still appeared every newpix, but they were repeats of old frames so began to be known as oldpix instead.
The frame displayed is either 3090, 3091, 3092, 3093, or 3094. There is a complex looping cycle looping between these 5 frames, the looping cycle changing periodically. If frames 3090-3094 are labelled A-E, here is a list of all frames displayed in order since the end of the comic: http://xkcd.mscha.org/epilogue.html.
slinches found an apparent pattern in the epilogue sequence.
This post compares the looping cycles for 2013 with the looping cycles for 2014