The 2826A is equivalent to the 2500B in terms of the co-axial parts, beat rate, etc. The 2826B is equivalent to the 2500C in terms of co-axial parts, beat rate, etc. So this gives you the most up to date version of the 2-level co-axial escapement - still not a 3-level, but the best 2-level design.
On the parts, most of these are regular service parts that are replaced on most watches. In particular the case parts,. so gaskets for the crystals, case back, etc. New crown, new case tube, new HEV. This is all standard stuff to be replaced. The stem is still in the old crown because the watchmakers won't take time to remove it from the old crown and use it again - technically there's usually nothing wrong with the stem, so this is just either laziness, or a time saving measure depending on how you look at things.
For the bracelet - common to replace the worn pins and tubes. It is unusual to see the pins for the fixed links showing, at least in my experience.
On the movement parts, the entire barrel is replaced, again mostly to save time, as usually all that requires replacing is the mainspring. The co-axial parts wear (so much for no friction!) so replacing the co-axial wheel and pallet fork is not uncommon at all (these are parts that are rarely replaced in a lever escapement movement by the way, even though the lever escapement is supposedly inferior). The other wheel are likely replaced for wear on the pivots, so the third wheel and intermediate wheels are common to replace.
The reversing wheel and the reverser are replaced from the automatic winding - again hard working parts that are often showing wear. Looks like maybe the ratchet wheel driving wheel, and some other auto wind and barrel bridge wheels there. A few of the wheels seem to have a lot of dirt in the teeth, so not sure what that is from. If they came out of the watch this way, that would be unusual. No idea what the setting lever was replaced - not a parts that often needs it unless it had rust from a faulty crown seal...but it doesn't look rusty.
Curious about two parts I don't see there. One is the bearing for the rotor, and with all the worn automatic winding parts I would have expected the bearing to be replaced also.
The second one I'm very surprised not to see is the hour wheel. This movement has the one hour jumps of the hour hand, and that wheel fails over time, and I always replace it at service. I thought Omega did as well, but maybe not...
Cheers, Al
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