"In" usually means the rated nominal current or the sensor size.
I would recommend you read instruction and operating manuals of the breakers and their trip units in question. Especially if the breaker has an adjustable electronic trip unit. You need to differentiate between sensor rating, plug rating and Long time pick up settings and where do they apply.
I've never seen In on a generator nameplate, but I haven't seen everything yet. I would assume In to mean Neutral current. It may be an indication of the maximum unbalance that the generator may accept without excessive rotor heating. I would be more comfortable seeing the whole nameplate. Seeing everything in context helps to understand unexpected ratings.
Bill
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"Why not the best?"
Jimmy Carter