Ah yes, codesharing. The last desperate attempt at trying to get on a flight operated by someone they normally couldn't fly. What I'm saying is, you definitely aren't the first to ask that question :P ... codeshares are purely done for marketing of revenue passengers. With nonrevenue, it doesn't mean anything, so you can't use that as an excuse. The one exception is IAD-MAD-IAD. This route is operated by Aer Lingus, run just like how SkyWest and Mesa run regional routes for United Express, but with a big plane instead. You can fly that one round-trip route, along with those express flights.
And now, the good news. You work for UA itself, right? Or another company contracted by UA that gets flight benefits, like one of the regional carriers? When I started working for SkyWest, there was a 2 WEEK waiting time, I think so that our HR/Travel department could have enough time to send the names of everyone covered over to United. I just started a new job with United about a month ago, and my previous seniority had no impact whatsoever on this. I believe I had benefits right away, I did use them a week or two after starting.
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