All of the frozen grape must pails sold by Grapesforwine.com have labels indicating the sugar levels on the pail as well as on the listing itself. However, you should remember that these readings are taken either during the harvesting process and/or during the staging process for filling the buckets. The vineyards cover a large area and certain pockets differ from others. The particular buckets of frozen grapes you receive are each unique and for that reason should be remeasured prior to and during the entire winemaking process to ensure your wine comes out how you want it.
Remember to mix the fully thawed must prior to measuring the sugar of your must. Sometimes rehydration is necessary due to some losses during the freezing and thawing wine grapes process, this is completely normal and must just be adjusted for.