Moto VHF and UHF systems all have three "ranges" of frequencies and channel numbers. Sometimes only one or two are listed because they are all that appear to be used at the time. In this database, the "offset" is listed (sometimes confusingly interchanged with the step, or spacing).
Offset is the lowest channel number on the range in quesion ("channel low"). "Channel high" will be the last channel in that range.
Here is an example. Suppose a system has offsets 380, 540, and 702 for its ranges. The first channel low/high set will be 380 and 539; the next will be 540 and 701; the last will be 702 and 759.
If you only see one offset listed, make channel low that number and channel high 759. That's the best you can do with available info.
Dave