potassium sorbate is also referred to just as sorbate. Potassium metabisulphite is called k-meta, sulfite, cambden tablets and more I'm sure.
Sulfite and Sorbate should be added together as they are stronger together then individually. After a month it's hard to say if your sulfite levels are still strong enough to help the Sorbate. Only a SO2 test can tell you for sure. You need to add both when back sweeting to prevent any recurrence of fermentation.
If you are bulk ageing, I'd say leave be for three months then add the sulfite/sorbate and sweeten. If you're going for an early drinker, you'll most likely be fine resulfiting early. Just let the wine breath a bit before drinking.