I ordered a miraculous medal from the National Shrine of Our Lady of the Miraculous Medal, which stated that the medal has been blessed at the shrine. However, I've heard that sacramental objects lose their blessing when they're sold or mailed. Is this correct? The selling part makes sense to me to a certain degree, but I don't know if my purchase of this medal counts as it being sold or if it is considered a donation to the shrine? Also, the site doesn't make it clear if the medal was blessed prior to be being sold or afterwards, which it seems would make a difference.
Basically, I find myself a little confused and would appreciate if someone could show me an official statement made by the Church on these issues (i.e. somewhere in canon law, etc.). I don't want to ask my parish priest to bless this medal if it has already been blessed, but if it has somehow lost its blessing then I would like to have it blessed.
Thanks in advance for any help any of you may be able to give me on this matter.