I think you will find the aircraft actually is 'imported' each time you land in a different country.
You are right however there are various rules to avoid/defer paying duty/VAT for legitimate transit aircraft. There does appear to be a dwell time limit that the EU uses to deem a privately operated (defined more narrowly than not AOC) foreign aicraft owned and operated by a foreign (non EU in this case) national and never carrying EU nationals or goods as having been imported but that doesn't mean it is a general rule.
All of which is irrelevant to the OP who is in an EU registered aircraft, staying within the EU.