The current highest value is stored beginning at byte 73 decimal. The next value is determined by adding to it. Here is a simple Delphi function that returns the current autoincrement value.

function getAutoInc(filename : string) : LongInt;
var
   mystream : tfilestream;
   buffer : longint;
begin
     mystream := tfilestream.create(filename, 
                 fmOpenread + fmShareDenyNone);
     mystream.Seek(73, soFromBeginning);
     mystream.readbuffer(buffer, 4);
     mystream.Free;
     getAutoInc := buffer;
end;