The two dots under Dr are found on 10 mold variations of Hostetter's. Your example appears to be a vintage 1873/74 bottle. The McCulley Co used that mold, or a similar one, from 1873 to 1884. They also had a Hostetter's mold with a line under Dr that was used concurrently. Mold variations, however slight, are numerous in the glass houses that blew those bottles.