There are only two generations of the -200: the CEO and NEO. The older craft in question are part of the same generation occupied by the end of line CEO's LH and Peach are receiving currently.
Nothing has changed in the frame or systems since November of 1988 - even Airbus admitted a brand new NEO is 95% parts compatible with a 30 year old -200.
There are four generations of CEO structure. Someone will have to provide a link.
Latest generation has Sharklet reinforcement built in by default.
Mid generation is retrifitable to Sharklets, but must add significant weight (and it takes time) to retrofit Sharklets.
Earliest A320-200 structure cannot support winglets and requires expensive modifications to get past 48,000 FC/60,000FH
A320-100 structure. 48k cycle/60k FH limit if double biggie. Others required weeks of work for life cycle extension (often not economically viable).
Then there is a the NEO.
I'm not aware of a single aircraft to get past #500 without significant structural changes. The A330 and 777 compete for the record in the extent.
Is the A320CEO on its 3rd or 4th generation of avionics? The 737NG underwent two hydraulic system redesigns to cut weight and maintenance.
The NEO is the first to significantly change wing aerodynamics (cross section changes to increase laminar flow).
The new structures can be retrofitted, so old parts are no longer inventoried for spares. Except for the keel changes. But unless an A320 is less than 7 years old, if you damage past doublers, the plane is scrap anyway.
Didn't the 763 ER pretty much stay identical structurally between 86-14?
Pretty much is challenging to define. Did it undergo less radical changes than the A320 and 737NG. Yes. There was an engine pylon structural improvement , minor change to the canoes, nacelle improvements, and the major aft pressure bulkhead changes (shocked me how many in service 767s had this retrofitted by replacing the aft pressure bulkhead). But nothing of the magnitude of the 737-900ER aft bulkhead or redo of wing structure the A320 underwent for Sharklets.
IIRC, the 787 is on the 3rd wing/body join configuration. Post A340, dramatic internal A330 structural changes to increase MTOW and the A330NEO build off the prior wing, but so many parts are thicker, it looks like the same structure, but isn't.
So no, I'm not aware of any commercial jet aircraft in production for a decade that didn't undergo significant structural changes.
For the A320, Airbus is looking to replace aluminum parts with 3D printed titanium. The old assemblies will just become obsolete and instead if replacing a few parts, a new sub-assembly will be purchased and installed.
Airbus has a program to remove several hundred kg of weight from the A320 per year. That requires structural changes.
The A321xLR will be the greatest structural change yet! The wingbox is getting modified to create"free" fuel space. It wouldn't surprise me if Airbus didn't take lessons learned to extend the A321xLR to 90,000 FC/180,000FH. Not that anyone cares about that future a life.
But if the maintenance intervals could be, incrementally, increased by 50% or in other words reduce overhaul costs 33%, airlines will pay a premium for that.
What is the weight of structural reinforcement to meet the extended maintenance intervals for the A320? I've heard rumors to bring old structure up to new structural limits is on the order of 180kg of doublers throughout the old A320 (I've heard 40kg more for the A321). Does anyone have a link?
To be clear, Airbus has done a great job of continuous improvement. Old aircraft being upgraded need weeks of work to perform significant structural upgrades. This is normal. I fully expect the A321xLR to go for the 50% life increase. I expect eventually the A320 to gain that structure too, but after a few year lag. From what I see, this upgrade is not economical to retrofit. C'est la vie.
Winter is coming.