If you do find that there is no insulation and need to cut holes to blow in some here is what has worked for me. I just cut a circle out of a piece of plywood about six inches across and use that as a pattern to mark the holes to be cut on the wall. Then take a jig saw and turn it to a forty five degree angle and cut out your circles. It would be a good ideal to number them so you know which hole they come from. After blowing in the insulation just take the drywall circles that you cut out and put them back in the holes you cut them from. You will need to bed the holes with drywall compound and then stick the circles in. After that all you have to do is tape over the holes, sand and paint. Its real simple and a hole lot easier than measuring each hole to patch the drywall back.