My take:
data have;
input col1 col2 $ col3 ;
datalines;
1391 catA 84
1392 catA 25
1475 76 35
;
data want;
set have;
date = intnx('month','01FEB1885'd,col1,'b');
format date monyy7.;
run;
Basically did a reverse backdating your given example for 1391 to establish a base date to use the Intnx function, which increments date, time and datetime values, the set that in code. The default day of the month for the date will be the first day of the month.
Please note the data step code to provide example data. Also, placing such code in a text box opened with the </> preserves text format when pasted and sets thing aside from the general narrative.