If you are willing to offer some wine for the purpose there is a way to calculate the alcohol content of a wine without knowing initial SG.
Here we go.
You will need a test tube and the hydrometer.
First pour some wine in the test tube and measure SG.
Also mark the exact level of the volume.
Next boil the sample till half the volume has evaporated. Now you are sure that there is no alcohol in the sample left.
Pour it in the test tube again and fill it up with water until you have reached the exact same level again. Stir well.
Now measure the SG again.
Enter both values in fermcalc.
http://web2.airmail.net/sgross/fermcalc/fermcalc_applet.html
Look for the upper tab alcohol and then choose in the lower tab the 'boiling off method'.
Now from the figures you have being the SG when boiled off and the amount alcohol you should be able to calculate how much sugar was initially in the must........
Another way to calculate alcohol would be measuring SG with a hydrometer and measuring with a refractometer.
Again use fermcalc and now choose hydrometer+refractometer method. Gives also an estimated alcohol percentage fromwhich you can derive initial SG.
But then you would need a refractometer of course.....
Luc