If you said it was a Tango fare, then you've hit one of the major changes recently introduced, which is the segregation of economy into a low fare Tango category, mid-priced Tango+ and flexible Latitude. Tangos don't earn full miles, though at least internationally earn status miles. K still shows as an upgradeable Tango+ fare, but it has been downgraded by LH and I suspect AC may be following.

So please confirm K is still showing on your tentative booking as Tango+ and not Tango. Otherwise you'll be severely short changed on your MR!