... complete with additional postage. Because of the glitter ...
If the cds is on the card, and not on a clear wrapper, this does not satisfy.
The rule was that glittered postcards would travel under cover and at the letter rate
While someone may have misunderstood the rule (known to happen), or implemented it poorly (known to happen), other possibilities include laziness (sender had only 2c letter-rate stamps at home) and philatelic contrivance (please hand-cancel and I will hand-deliver).
/s/ ikeyPikey, who looks forward to an SCF Yearbook caption that reads "Most likely to become wt2."
Thanks to http://www.uspostalbulletins.com/
US Postal Bulletin item from Seminal Year 1907:
Comprehensively re-stated in 1946 as: