Please, enclose the the regex in <code> ... </code> tags to be readable.
Also, please specify what strings the regex does not match but should - it works for me: 
perl -E '
    $R = qr/\d{2}[-._]\d{2}([-._]\d{2})*/;
    say "$_ ", /$R/ ? "Y" : "N" for qw/1-2 1-20 11.20-1 11.20 12_30.99
+ 000_00_000/'

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Maybe you miss the anchors? Put ^ at the beginning and $ at the end of the regex. Also using ? instead of * might be desirable not to match strings like 12-12-12-12-12-12-12.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: Regexp problem by choroba
in thread Regexp problem by agaved

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