More weirdness.
I don't know if there is an actual term for this. If so, correct me. Here is Netherlands Indies - Japanese occupation issue for Java, Scott #N10:

The Japanese inscription is (partly) crossed off in indelible pencil/copying pencil. I suspect but obviously can't confirm that this was used during a period after the surrender. The cancel is murky but is at least the boxed type used in the Indies.
Sure, this could have been done privately by a revolution-minded clerk or later by some collector's evil little brother. But I've seen other similar things from elsewhere that could have been used during an interim period during a revolution or regime change. For example:
- Laos #C89 Orchid with "Royaume de" neatly crossed off in ballpoint. Usage would jibe with Pathet Lao and N. Vietnamese control of parts of the country c.1972 and later. I have this packed away somewhere (yeah, yeah).
- Iran #667, etc. Ahmed Shah Qajar defins. He was actually out of power by the time this issue was released in 1924-25 and formally deposed in October 1925. I've seen but was not able to buy some used low values of this issue with his head covered with cut pieces of gummed brown paper tape, cancelled over stamp and tape.
Again, these were just single stamps suspected of provisional-type usage, but without provable usage. Covers would be more convincing, covers to foreign destinations better still.
You could maybe add in the rubberstamped issues for Ghana on Gold Coast stamps, Bangladesh on Pakistan issues, German overprints on Czechoslovakia, German Hitler heads with head blotted out, etc. but I've seen only favor-cancelled covers, lots of dubious mint stamps plus proven fakes.
So, do you have any similar suspected-to-be-postally-used items out there?