Different companies do and have had different policies.
At the time, valve seals, gaskets, etc., were not kept for inspection, etc., by Oldsmobile or Chevrolet Indeed, few things were, e.g., carburetors, radios, etc. This, of course, is one of the reasons that Oldsmobile could submit thousands of fraudulent claims for this issue.
Times do and have changed. Who knows what today's policies are, but I can attest that things became worse rather than better, at least for some time.
SDT
Kubota requires dealers to retain ALL warranty replaced parts for 120 days. 6 months. And this is AFTER the claim is processed/paid--which can take months on it's own....
The downside to that is.....in the case where I worked, 6 months of warranty parts adds up QUICKLY, and it becomes a pile (a big pile) in one month, with no good place to put them. One place I worked had a neat shelf that spanned an entire wall of the shop (about 70 foot length) specifically made and labeled for warranty parts, by date and manufacturer (since we had 4 brands). It worked well as long as it was maintained. Every so often we'd go through and trash the parts that were out of date (over 120 days in kubota's case). BUT--it never fails, the day after the garbage truck runs, Kubota sends you an email requesting either photos or return of the warranty part that is out of date. So we resorted to keep them typically for about a year. Cleaning around Christmas. You talk about a pile of parts! Keep in mind we (or "I", more specifically) were doing around 190-220 labor hours per month. We stayed busy with warranty and customer-pay work. Too busy. My body paid the price too. You can do some math on that. I was being paid around $20/hr plus a bonus. Dealer was bringing in around $20,000/mo off of my work, paying me $4000 (gross). As for me? Nary a day went by that I didn't HURT, everywhere from head to toe. 20,000-22,000 steps/day (pedometer-prescribed). Work consumed me, totally. Get home from work, rest for hours. Not much energy left to cook dinner so I generally would eat frozen or prepared. Not good diet which made it worse. Sleep a few hours do it the next day. 5 or 6 days a week (2 saturdays a month) with a few hours off, 2 wk vacation and could not take more than 5 days at a time (so people wouldn't take all 2 weeks at once). No air conditioning in the shop, 105-120 in the shop daily poor electricical service such that when you plug in a couple fans, it trips the breaker. Last 8 months (Feb-Oct 2020) with poor heaters, which wasn't a big issue except for Feb/Mar/part of April)--it might have reached 60 if it ran all day and the doors STAYED down (rare). The concrete work was at best, poor...nothing level, standing dirt, rough concrete surface, cracked everywhere and a pair of streams that ran UNDER the foundation (right under both of the 9000 lb 2 post lifts). Keep in mind I take lots of pride in my work and I don't do poor work, period. I want 100% customer expectations to be met. I couldn't do that with the facility we had. Level a mower deck? LOL! It wears on you. After 3 decades, I went in on one saturday and said I've had enough, put my notice in and 2 weeks later left and haven't looked back.
side note, I was talking to a guy I used to work with and we had a pretty good conversation about time, life, and work. One thing he mentioned was that all we have (as humans) is time. We sell our time to our employers. If all we have is time and time is our life, then we are selling our life to our employers. Interesting thought, at least I thought so.
They've (kubota) gotten better but not by much. Now they're requesting digital photos of the unit, the serial number, engine number, AND the failure in question, then the part that caused the failure (causal part). I have know of other dealers who've used hybrid phototography which is wrong. IOW, they'd take pics of the unit, serial number, then take pics of someone else's failed part on a different machine or out of the warranty parts pile. This was done when I worked with Deere, although I heard of it at one of "our" (dealer chain) kubota dealers. I always lived by doing right, and not teasing a rattlesnake.
I'm sure they have good reasoning for doing things that they do but as a former tech, some things that they wanted were asinine. Like returning of a mowing deck to the warranty dept for inspection--even after pictures were clearly sent and the claim paid. They'd get the deck back (and no they don't always pay shipping/freight) and deem that it was customer abuse/neglect and at that point they debit our account the amount of the claim. Keep in mind, it was 11 months after the claim was processed and paid. It happened too often. Once is too often. But on the flip side I have experienced times when a repair was a cut-and-dried case of neglect, thus not warrantable, and we (I) would submit it as a pre-authorization for warranty coverage, knowing full well that they wouldn't pay for it. Days/weeks go by, customer's paid and picked his stuff up, and then warranty department authorized the repair under warranty (or sometimes as a goodwill). So then the issue there is having to get in touch with the customer who is probably not happy (they won't answer the phone) and (2) getting the accounting department at the dealer to cut a check for a few times thousands of dollars. Of course the customer if you could get in touch with them was ecstatic and immediately showed up for a check regardless of whether the dealer had the funds available or not. BTDT. After payroll was done at the little place I worked for, wasn't much left.
People just think that warranty is cut-and-dried and as you can see from just a few examples, it's complicated--but necessary. I advise most folks that if you have an issue, if it's an easy fix like tightening a bolt, just take care of it on your own if possible. If its something that is more involved, get the dealer and the manufacturer involved keeping in mind that they don't cover abuse, neglect, lack of maintenance, bouncing off of trees, rollovers, and transportation to and from the dealership. If you are on your Kommander Z251 and run it up a cedar tree trying to trim it and break the belt, chances are VERY good that you're gonna have a hard time getting coverage under the limited warranty, in those cases, fix it yourself or pay the dealer.