Do you own and know how to use a SWR meter? That is the only way you can check for sure. Also the SWR may change depending on where you place the antenna. The top of the roof is best, second to the trunk lid, if you have one. If you don't own a meter, borrow one from a local ham and try the antenna out, testing in the center of the 10 meter band first. You have a little bit of length adjustment that can be made to the rod with the set screw. Good luck. Let us know what the reading is. Anything below 1.5/1 is good!
I have had good luck with these antennas without shortening the rod. Hopefully, the previous owner was a perfectionist. With the full length rod it can be used on 10, 11 and 12 meters. That is why I don't shorten mine!