For 73 3-5 series, the oil qty will vary depending on temp, coldsoak and time since shut down. In my experience tho variance will be 3-4 ltrs maxim. There should always be a significant qty showing and at least the min recommended for eng start (a lot less than the scope of normal operating qty's including variances). I believe that the eng 1&2 oil qty are both supplied by the same power supply, there fore, if one eng is registering a +ve qty, the other is powered (but not necessarily receiving valid data). You will then have to decide is you have a case of invalid/nonexistent data to gauge (some have a light blue off scale fail needle index) or a correctly indicated low qty.
Restarting a oil deprived CFM56 will quickly (5-10 mins) lead to the most expensive auto shutdown you will ever see on a 73. Having said that, as a last resort thats 10 mins of thrust which you might not otherwise have had!
Hope that helps? Typed after a busy day.......
Mr L