I spend the last hour and a half following up on old Perl5 bugs. I'm not quite sure how many I went through (20?), but it didn't help on the graph at all.
No patches required, just go through the bugs and ask the original submitter for more information or to re when it's relevant and mark them in RT with the relevant versions of perl. Depending on the bug I would leave it "open", mark it "stalled" or "resolved".
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Wow, that's some interesting graphing. Thanks!