If all you ever did with the plugin was assign series values by completely ignoring whatever existing values the series had, then yes it could do that.
However it does attempt to preserve whatever existing numbering strategy the series has. So if I have books in a series of 1, 1.5, 2 and being them up in the plugin, the default behaviour is to keep them as 1, 1.5, 2. Were you to type "2" as the start number, the books will become 2, 2.5, 3 - not 2, 3, 4.
That is only possible thanks to some complex logic which all goes to pot if the user were allowed to type 1.1 or 1.01. Or if the existing series numbering started at 0.5 for instance. Too much effort for the sake of a mouse click on your part
