Is this a proof or a business strike?

As a mere yout, I bought a 1970 proof set off of eBay with a rare No "S" dime. I just hauled the set out for the first time in 15 years, and I'm not so sure the dime wasn't switched out now that I look at it (there's some ambiguous evidence of tampering at the seam).

Denial's my favorite defense, so I thought I'd better ask objective eyes. Is this a proof? What dya think:

 

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Sorry. I misspelled "Yute."

 

More defined pictures especially where the mintmark should be needed for closer inspection.

 

Here ya go. What are you looking for?

 

The mint mark was moved to the obverse above the date. 1964 was the last year the mm was on the reverse.

 

Example

 

Looks like a proof to me. Here the one I found a while back:

 

Thanks, all!

 

Yes, it's a proof.

 

Little dirty proof

 

It would be worth sending to NCS for conservation.