The second solution has a problem: each chop reduces $_ by one character until $_ is the empty string — which is what gets printed when $n is 65. My fix has 59 characters:

But the first solution can be reduced a little to 54 characters:

#23456789_123456789_123456789_123456789_123456789_1234
perl -nlE"$n=0;map$n+=$_-96,unpack'C*',$_;$n==65&&say" words.txt
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:-)