Some things are posted on here by people who then realise it's against company policy or just risks getting themselves in trouble saying it. Mentioning specifics of aircraft mods is not very clever to do, even though you might think it's relevant.
Some aircraft types have non-structural fiaring parts that are made of lightweight fibreglass and in places where you wouldn't think they'd make a difference. Spares are not always kept and thus occasionally you'll see a gap and bit of light green paint on the back of bulges or fairings on wing trailing edges or undercarriage legs, etc. The original part may have cracked and been removed and something called a configuration deviation List is carried in aircraft manuals to allow operation in these cases while the new parts are painted up and sent out to meet up with the aircraft asomewhere where they and engineers co-incide.
Happens for all types and companies. Some of these pieces actually cause a significant penalty as the drag increases. Hence the weight reduction for performance. Actually giving details for a particular company or aircraft type is not best practice- as it changes from time to time and is calculated when required. You just need to know it happens and is cheaper and less annoying than grounding the aircraft and cancelling your flight.
I hate leaving bags behind. However, it's better than leaving passengers or finding yourself running low on fuel with nowhere to land.....