Oct 28, 1972 - HoustonPreliminary System Review (stage I)
note, the ASTP emblem was introduced only on March 1974 thus this cachet in not 100% "clean"
Aug 12, 1974 - MoscowCosmos-672 launch - unmanned analogue of Soyuz-19 spacecraft
ASTP Pre-launch covers
Jan 12, 1975 - HoustonSoyuz-17 docking Salyut tracking by NASA. Although this cover shows the event as part of ASTP preparation, Soyuz-17 has never been tasked to perform any ASTP activity (at least officially).
Feb 11, 1975ASTP spacemen arrive at JSC
looks more like a souvenir card with no stamp and postmark, but signed by Alexey Leonov