It will surely be helpful if you posted scans of some of the stamps in question. Are the postmarks all from the same place and the same day? Maybe the postmarks are "favour cancels" (i.e. handbacks), or the postal employees were just asked (maybe even on several occasions) to cancel the stamps carefully.
At the end of the series entry in Scott is a notation re CTO issues with printed cancellations vs. "postally used" stamps.
Based on my experience with various CTO issues from Eastern Europe, the postmark is frequently applied across the corner of four stamps. And as such appears as a quarter circle on each issue. Plus the ink of the pre-printed cancellations is often shiny in appearance.
In looking at the Tanzania "fish series, it appears the postmarks are applied at or near the center of the stamp and feature concentric rings. Plus the associated ink is dull in appearance.
Does anyone have experience with this series stamps? And if so, what is the supposed CV premium for "postally used" stamps?
Thank you.
re: Tanzania: 1967 - 71 "Fish" series
It will surely be helpful if you posted scans of some of the stamps in question. Are the postmarks all from the same place and the same day? Maybe the postmarks are "favour cancels" (i.e. handbacks), or the postal employees were just asked (maybe even on several occasions) to cancel the stamps carefully.