Smart Meter Interface Script - Validate values before sending them

[MStapelfeldt]

I have a LK13BE6067x9 smart meter, but I think this is a general Topic/Question:
While reading the values in script

1,77070100010800ff@1000,Gesamt kWh bezogen,kWh,Power_total_in,1
1,77070100020800ff@1000,Gesamt kWh geliefert,kWh,Power_total_out,1
1,77070100100700ff@1,Verbrauch aktuell,W,Power_curr,0

I want to manipulate the values, to validate them and avoid wrong readings. I'm able to do this in HomeAssistant or ioBroker, but why send wrong data, if it could be done on device directly?
So what I'm trying is a simple

if 77070100010800ff@1000 < lastbezogen+1 && 77070100010800ff@1000 > lastbezogen
    1,77070100010800ff@1000,Gesamt kWh bezogen,kWh,Power_total_in,1
    lastbezogen = 77070100010800ff@1000
else
    1,lastbezogen,Gesamt kWh bezogen,kWh,Power_total_in,1
if 77070100100700ff@1 < 5000
    1,77070100100700ff@1,Verbrauch aktuell,W,Power_curr,0
    last_verbrauch = 77070100100700ff@1
else
    1,last_verbrauch,Verbrauch aktuell,W,Power_curr,0

This would filter out all very strange readings, for example have a current Gesamt kWh bezogen of 20.000 and next reading 453.455, which is not possible.
I tried to use = 16 as Filter but it doesn't help.