You fed one colony *1 litre*? Thats next to nothing, enough for a decent colony to keep it alive less than a week (well less actually, depends on what they had and how big the colony and what rate it was breeding at). A sisnificant proportion of that will have been used. For such a small volume of syrup one also assumes (subject to being corrected) that it was home made syrup. This will ripen down to maybe 0.6 litres, some of which the bees will use in processing it, so lets just say 0.5litres.
You have a hive that is filling its second super, so the presumption must be that he bottom super is full or getting on for full, otherwise the second one would not be there. It will thus contain about 10 litres of honey. Even if ALL the syrup was stored in the supers, and *none* used, you have a maximum of 5% syrup in the super, and probably a good deal less.
During spring expansion bees evict stores from the nest into the early supers regularly and winter stores (yes I KNOW some of you never feed, but most do) get moved upstairs, and are ultimately extracted.
At such low concentrations it is simply not noticeable. If what you fed truly was 1 litre then I think you worry too much and should just get on with it and extract. You will have somewhere up to 5%, but more likely 1 to 2%, syrup derived 'honey' mingled into your product at which points its both undetectable and undiscernable. If many are being honest probably no different from a lot of spring product.
Different matter if you had shoved 2 gallons into the supers.
