about the variable 'processed_full' in Stock_NeurIPS2018_SB3.py

may someone explain the purpose of the codes from line 63 to 73?

the missing dates in the 'processed' are added to 'processed_full' and then deleted; finally it seems that the only difference between 'processed' and 'processed_full' is the position of column 'tic', what else? if it is, why not just reorganize the columns of 'processed'? 😂