My understanding of OLC is that it's a single piece of cardstock folded in half to make the card base and that's it, no extra cardstock. Where I differ from Lydia's understanding is that I'd say (minimal) embellishing is OK.
Susan (Lateblossom here at SCS) co-hosts a weekly challenge for OLCs, you might find the "rules" there useful.
Here's the latest challenge and you'll see that Susan has bling as well as stamping on her OLC.
HTH!