Hi Adrian,
I've had a read through what you're trying to do, and while I don't fully understand how you're storing this data, I believe what you're trying to do is put students in to a "Gold" class if they have above 1500 points etc. You then want to display the gold certificates in Frog if they're in the "gold" group. I think there will be better solutions to this but if you can get the correct students into the correct groups in SIMS then this should still work. However I would advise against using House Groups as they're not intended for this, instead I'd recommend the "Other" group option in the extractor. The "Other" option for SIMS is user groups so feels more like what you're after. If you can get these groups correctly created and populated then displaying the certificates to the user in Frog should be a possible with a FrogCode widget.
You can check the FROG_Groups_Others report in SIMS to see what would be extracted if you were to run it.