The model 99 was manufactured for approximately 40 years and had numerous versions and subversions. In the early days of portable electric machines, the knee-bar and foot pedal were both popular but over time the knee levers were phased out. At a guess, your model is most likely a 99-13.
For the first 20 years or so, 99s did not have a stitch length lever, but instead used a silver turn-knob located on the arm just in front of the hand wheel and just above the gold Singer badge. These machines did not have reverse (No Singers had reverse until the mid-1930s or so). A company named 'Revco' made a popular add on for Singers that added a reverse and these pop up on eBay now and then.
These machines did not have a reverse because Singer considered 'backtacking' an inferior technique to 'drag-tacking' which does not require reverse. Singer added reverse to their models only after competitors made reverse stitching a selling point. In fact, nearly all Singers were capable of reverse, Singer simply made it impossible to set the stitch length to a reverse position. The mechanism could do it perfectly well.
For the first 20 years or so, 99s did not have a stitch length lever, but instead used a silver turn-knob located on the arm just in front of the hand wheel and just above the gold Singer badge. These machines did not have reverse (No Singers had reverse until the mid-1930s or so). A company named 'Revco' made a popular add on for Singers that added a reverse and these pop up on eBay now and then.
These machines did not have a reverse because Singer considered 'backtacking' an inferior technique to 'drag-tacking' which does not require reverse. Singer added reverse to their models only after competitors made reverse stitching a selling point. In fact, nearly all Singers were capable of reverse, Singer simply made it impossible to set the stitch length to a reverse position. The mechanism could do it perfectly well.
