Nothing to do with all you have mentioned. An API certified engine oil either synthetic blend or fully synthetic can be driven up to 10,000 KM. The proper way to evaluate is to take oil samples at different odometer readings, get the lab results and go on. Since these have already been established which is to be 10,000 KM being on the safer side.
We here in Pakistan are reluctant to do so as we change mineral based oils at 2500 to 3000 hence the same we do with synthetic oils, doubling the oil change interval.
The oil change interval for API approved mineral oil is 5000 KM. So, cutting short, the API approved synthetic oils wich we discard at 7000 or 8000 can be used safely till 10000 KM.