Out of interest, what does happen to the delta when the values wrap around from 127 back to 0? Do you simply lose one reading? If they go from 125 to 8, you'd lose 10 strikes...
I believe you are asking how weewx handles counters. Hopefully one of the people with direct weewx knowledge can answer that.
Note: counters are a reasonably common data representation. Things like the rain gauges count tips. There aren't infinite bits available so at some point the counter wraps around just like a 4 digit meter (electrical usage, odometer, etc.) that rolls over from 9999 -> 0 or whatever depending on the number of digits it has.