Overlapping booking on different airlines?
 

I know that if one has a duplicate/overlapping booking on the same airline, 99% it will get cancelled (e.g. a booking for both 8am and 10am SFO-JFK flight on the same airline).

But what about two different airlines (specifically in my case, United & Alaska).

Do their backend systems talk to each other?

For reasons, I need to book both SFO - SEA (on Alaska) and SFO - PDX (on United) at the overlapping same time, and wouldn't know which one to take till the day-of. I will not attach my mileage numbers etc.

Are there any data points on cancellations in this case of the overlapping flight?

Neither will know nor care.

No back end integration - you're safe.

Given those are short flights with low cost competition - would it be comparable to book two refundable fares so you could cancel the one you don't need? (Would two non-refundable fares be approximately equal to one refundable fare). if that were the case, it might gain you more mileage credit and be easier to submit for reimbursement (assuming that is a factor).

Thanks. I'll check refundable but good to know systems don't talk just in case.

Yep, book away and use your FF numbers, nothing to worry about. And I agree, for those flights one refundable fare (cancel the one you dont use) could possibly be cheaper than two non refundable fares.