Some inverted overprints are the result of human error or carelessness. Sometimes, when the work of overprinting is carefully supervised, inverted overprints are rare. If they occur just in position 1 in a sheet, then it is because a worker has picked up a handstamp upside down. When he (probably he) realises his mistake, he turns the handstamp around.
Podillia Trident overprints are very rarely inverted. The work was clearly carefully supervised and errors easy to spot. In contrast, an inverted Armenian framed and unframed Z overprint does not look very different to an uninverted one. So non-philatelic inverts are quite common - but so are philatelic ones
Some inverted overprints are clearly philatelically-inspired, to create collectable varieties. This is true, for example, for Kyiv I Broken Trident overprints [Bulat 62 - 108] and as a result Bulat remarks "Inverted overprints exist on most of the above issue and are priced the same as normal overprints" - though from my holdings, inverts are not equally common. Indeed, to make Inverts as common as Normals defeats the object of creating a scarcer collectable variety.
But there are other things to say about Broken Tridents and I will do this in my next Post