I know it is not typical for hobbyists to use very high nic concentrations but why not allow the calculator to accept and save recipes that use > 250mg/ml nic?
I make large-ish batches and typically use 300 - 500 mg/ml nic and the calculator will not save my recipes as it is higher than the 250mg/ml hard limit.
This is by design. The calculator is made primarily for DIY’ers - no regular DIY’er should handle nicotine stronger than 250 mg/ml for safety - you could dilute your 500 mg/ml to 250 mg/ml to get around this?