ok so i figured it out.
somehow the first couple stock backups i made ended up in the TWRP backup folder on the internal drive of the phone.
the new backup was stored in the TWRP backup folder on my SD Card.
so after finding both locations, i cut the two stock backups i made and pasted them into the SD Card TWRPs Backup folder and BAM! they show up now in my restore option on TWRP.