Google showing some Turkish Air flights as SkyTeam?
 

Google flights and Matrix seem to bringing up some TK flights as SkyTeam. Anyone know why / is there a codeshare I don't know about / a way to credit some TK flights to SkyTeam? TIA.

I wonder if those are TK codeshares operated by Middle East Airlines (ME). ME is a SkyTeam member - so that could be the reason they are showing up. In that case you're probably better off booking them under the ME flight number and not the TK numbers. It may be possible to book them as TK - but then crediting them to DL may be difficult or impossible.

I'm not sure the reason but even if TK flights are booked using the ME flight numbers you will receive 0 miles on DL. It would need to be operated by a SkyTeam airline to receive any credit.

Origin/destination? Dates?

Search LHR-SYD on SkyTeam and you'll get QF flights in the SIN-SYD leg. Search ATL-TBS and you'll get A9 on the AMS-TBS leg. Those two legs are codeshare with KL. I've seen others with AF, CDG-GYD on J2 for instance. So I'm not surprised to see Google Flights giving you TK flights when searching SkyTeam. I know CZ codeshares with AA.

Lots of SkyTeam members codeshare outside the alliance, but to a much lessor extent than the other two alliances.

IST to CKZ via ESB was doing it for the past few days, but does not seem to be doing it now. Perhaps was because these were codeshares operated by a third airline?

Yeah sure. But we don't typically see these single legs available as SkyTeam flights. Usually, there's something going on with codeshares that causes Google to do this when we see it; occasionally, there's an arrangement that allows the flight to be booked on a SkyTeam partner; even more rarely, it will earn miles or have privileges!

Doesn't look like that here.