Danger buying Luxembourg Bridge issue

I don't know if this appeared as a subject previously,
but what's left of the 20 May 3-stamp Bridges issue, quantities of
which were stolen, have been overprinted.

The valid version of this set is comprised only of those overprinted
with the post logo. It is barely visible, comprised of only phosphor.
The Post can spot the unoverprinted values when they pass through the
sorting/cancellers and don't "light up" or glow. Then the letters
with stolen postage can be culled so that the post and law
enforcement can confront every user of stolen postage to learn from
what dark channels the stolen stamp was obtained.

It may be that the valid version of this set is issued in quantities
that are a lot smaller than normal, given that large quantities of the
three stamps are invalid.

Careful when buying these - you may get the invalid version
unknowingly.

LN in DC