You've hit on a sore point, for which I have no magic answer.
Both my partner and I spent our young years working with some serious electrical equipment, but outside of the construction/ licensed electrician framework. When we went to find work, we were shunned by firms, programs, and AHJ's- as if we had spent our early years reading Playboy! Our prior, well documented training and experience were completely ignored, and somehow the apprentice programs never found either of us 'worthy.' Journeyman card, Masters' card, Contractors' lisence now- and according to one program, I'm still "progressing nicely on the list."
So my advice:
-Apply to every program you can. There's no telling which one might call. Union/Non-Union....the choice seems to be more one of chance, than any particular reason.
-Take related courses at your community college.
-Apprentice programs often work with the local college to grant college credit for their courses....this means you can take the classes at your own expense. It's your college, isn't it? Sure, you won't be in the program, but they can't say you're not getting the training!
-Different jurisdictions have differing criteria...in our case, it was easier to be allowed to take the electrical contractors' test than the local journeyman test (so for a while we were working with a 'doctorate' without being allowed to try for the 'bachelors'). (And when I was finally allowed to take the local test, they used a code they had adopted two days before!)
Our backgrounds? My partner spent 20 years in the Navy, starting as an Electricians' Mate, and working his way to Captain- hitting every rank along the way. I worked in some pretty heavy industries, for a standards-writing group, and have belonged to the Inspectors' organisation longer than anybody in town. None of this experience counted. At one point, my partner held the lisence, while his employer was not legally qualified!
One employer told me age was a factor- to the horror of the trade organisation, who feared a lawsuit, and quickly insisted that he was incorrect! I literally had to spend eight years unloading trucks before my now-rusty Kleins were allowed to be used again!
No one ever said life was fair, or easy. Keep your eye on the ball, and keep on plugging away.
Some other contractors were present when I was asked how I got started. My reply was that, after I couldn't find anyone to hire me, I hired myself. Turned out to be a common reason!
