find -mtime -$a | xargs zgrep -il ''$b'' | xargs zgrep -il ''$c'' | xargs zgrep -il ''$d'' | xargs zgrep -il 'ST.997' | sort -u

example_file.dat
example2_file.dat
example2_file.dat.bak.1234567890
example3_file.dat
example3_file.dat.bak
example4_file.dat
example4_file.dat.bak.qwertyuiop

example_file.dat
example2_file.dat
example3_file.dat
example4_file.dat