if u wish just try this in your file

input "test.txt"

*******************************

Title: Mary moo-cow 856 invalid

Title: the mechanics 857 valid

Title: Mary moo-cow 858 invalid

Title: the mechanics 856 valid

Title: Mary moo-cow 859 invalid

Title: the mechanics 8500 valid

undef $/;
open(FIN,"d:\\temp.txt");
$str=<FIN>;
close($str);

while($str =~m#Title: (.*?) invalid#gi)
{
push(@arr,$1);
}
print "$_\n" for @arr;
[download]

output

***********

Mary moo-cow 856

Mary moo-cow 858

Mary moo-cow 859