I am a non-Schengen country citizen, but I possess a Spanish (TIE) resident card, valid until May 2, 2020 (issued in August 2018).
From December 2, 2019 to February 14, 2020 I will be staying in Hamburg as part of a research visit. I spent 23 days in France this summer (from July 26 to August 17). So in principle, I need to be careful not to violate the 90-180 day Schengen rule.
The company inviting me to Germany will be closed from December 24 to January 5. I can thus return to Spain during this period, so mathematically everything should add up.
My questions are the following.
How can I prove that I spent the period from December 24 to January 5 in Spain, given that passports are not scanned at airport check-ins for flights between Schengen countries? Can I have issues with this?