John O'Brien wrote:
Does anyone know what USPS' present position is with respect to the use
of non-denominated stamps on international mail ? Thanks.

From the USPS International Mail Manual, section 152.2a:

Nondenominated postage stamps (except for those that bear uniquely
domestic markings, such as First-Class Presort, Bulk Rate, Presorted
Standard, or Nonprofit Organization) may be affixed to postal items that
are sent to foreign countries. The value of such stamps is linked to
either a current or a former domestic rate (e.g., the “H” stamp has a
postage value of $0.33). Since the international postage rates are
always higher than the comparable domestic postage rates, mailers
who affix a single nondenominated postage stamp to their outbound
mailpieces must add additional postage to comply with the international
rate schedule. Note: The nondenominated Breast Cancer Research
semipostal stamp, which has a postage value that is equivalent to the
domestic rate for 1-ounce letter, may be used for international mailing
purposes.

= Eric