Yes, Jehovah God was referred to as Lord in the OT, and Jesus was addressed as Lord according to some NT verses, but this doesn't mean that there was no Holy Spirit who was God or the Father who was God. That would be impossible to argue, using the Bible, but the Triune nature of our God wasn't understood at that time. During the earlier days of his public ministry Jesus wasn't recognized as the Messiah, but his followers finally caught on to that as also the truth that he was really God as well.