to_char function returning wrong data

Below code has caused my data to be wiped off a table as my where clause depends on the below returned value.

If the number of weeks is 4 or 6 or 3 it returns correct value.

select to_char(current_date - interval '4 weeks','IYYYWW') ;   

201901

select to_char(current_date - interval '6 weeks','IYYYWW') ;   

201852

This issue can have a serious effect.

Thanks,

Sreeni