I think you're confusing two seperate issues. Cubana is known for thier higher luggage allowance, so I'm pretty sure you'd be fine with the 2 bags at 23kg. The other limit is an "import tax" that was applied by Aduana (Cuban Customs) for Cubans returning to the island.
There was a prominent sign on our check in desk last night in Holguin that said the Overweight charges were 9 CUC or $10 CDN, so that much is true .