Keep in mind also, that is you are thinking these are doubled dies, somethings to consider:
1. If they are hub doubled, they would not be flat with the fields. They would be raised just like the devices. Clash marks that are the outlines of when two die clash together will trade copies of the outlines from the other die. Again slightly raised or lowered.
2. If just a few letters appear, where are the rest of the letters? it is were a doubled die, all the devices would be moved also. Not just a few digits/devices.

Even doubled strike transfer the full set of devices on both sides of the coin:




So if the devices were struck on to the coin, where are the missing ones and the same thing would be expected to happen on the reverse.
3. Dropped letters: They are incuse on a coin. Letter was filling on the die and falls out and the strike will make an incuse device, either normal in shape or mirrored.





So seeing something on a coin that looks like something that is not raised on the coin is probably a stain.
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