Specifically, the timelocal function does not return values for the variables ($year, $mon, etc.).

Are you talking about Time::Local's timelocal, or about the localtime builtin?

Either way, I can't replicate the issue. Both seem to work fine with 5.10 here.

use Time::Local;

my ($sec,$min,$hour,$mday,$mon,$year) = (0,1,2,3,4,105);

my $t = timelocal($sec,$min,$hour,$mday,$mon,$year);

($sec,$min,$hour,$mday,$mon,$year) = localtime($t);

print "$sec,$min,$hour,$mday,$mon,$year\n";  # 0,1,2,3,4,105
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