Is there any confliction in dataset and sample period description here? Dasgupta,2019, p.2598 documented that they

consider all nonfinancial firms in Worldscope, Compustat Global, and
Compustat North America data sets from 1990 to 2012

However, they used the [-2;+5] event window (page 2600) around the law implementation day to examine the impact of laws on dependent variables. In their country list on Table 2 page 2599, the last countries that passed the law are Ukraine, Taiwan in 2012. Therefore, based on their identification, their data sample should be from 1991 to 2017 rather than 1990-2012.
Apart from that, the first country applied this law is US in 1993, therefore, the data source should start from 1991 (two years before the implementation day).
Dasgupta in the study says he is using also other event windows in dynamic estimations:

To  explore the  dynamics  of  the issuance  activities  and leverage  change,  we  create  dummy variables corresponding to the following windows around the treatment  year:  from 1 to 4 years before the  treatment; the  treatment  year  and  the 2 years  after  treatment; the  next 3 years; and  the years beyond.

with window 1 to 4 years before treatment it makes sense.
Dasgupta also uses diff-in-diff and for that you need to test for pre-treatment trends so that also can be a reason.
Dasgupta also says that cartel data are from some 2013 publication so probably there was no point in getting more data from compustat. If they miss any data for their main variable of interest after 2012 then they can't run regression on longer than 2012.