Lets talk Ethanol fuels

[West TX GT]

Where I live the station guarantees e70 or higher. My question is if I get tuned for e70 and a month later it is really e85, will it be a problem? Like run too lean?
Occasionally they run out and I would have to get 93. Switching over tunes wouldn't be a problem but if there was a little bit of ethanol left in (like 20 miles to empty) would it cause problems?

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[SolarFlare]

Where I live the station guarantees e70 or higher. My question is if I get tuned for e70 and a month later it is really e85, will it be a problem? Like run too lean?
Occasionally they run out and I would have to get 93. Switching over tunes wouldn't be a problem but if there was a little bit of ethanol left in (like 20 miles to empty) would it cause problems?

Yes, short term trips will show adjustment but final AFR will stay as it was.