I know of at least 1 case.

Individual spent 6-8 months Delta. Left for FedEx..was there less than a year do not know exact time. Got another interview at Delta. I met him in the interview prep course. I don't know if I got hired...but he did get an interview so you know what they say. It would seem to me that if there was some boycotting procedure in place his app would have been blocked and never would have been invited back......

I got to admit I was kind of shocked with both him and them

Nice guy though...and I hope it worked out for him.