^Yep. It was used consistently in dialog, and I think it was on a lot of the set decoration (computer screens, those individualized badges they put on every bridge, that sort of stuff).
For Earthforce ships it was but not the Excalibur it seems. As near as I can tell, the opening credits is the only place the ship is refereed to as an "Earth Alliance Starship." It's never called either this or the "EAS Excalibur" is dialogue. Gideon only ever calls it the the "Starship Excalibur."
It's certainly a bit odd when the only contradiction is in the title credits and give that it's in every episode you'd think it'd count for more.
Thing is that (strange as it seems) the opening credits are just flat wrong. The Excalibur wasn't and EA ship and never was. It was built in secret by the ISA co-operation with Earth and Minbar with the intent of them being the first in a new fleet of Ranger ships. It only ended up in Earth hands later and only then on loan to the EA. So no, it's defiantly not and Earth ship.
I suspect this might have something to do with TNT who as I recall kept pushing to distance the show away from it's intended connection with the Rangers and more towards a show about humans finding aliens and shooting at them. On the one hand it might just be that the opening credits where being necessarily simplified--it is after all not the best place for a pedantic description of the ship's unique status.
Incidentally, I think I saw a scan of thst prop quite a while back--I think it was a printout Gideon holds at the start of 'The Long Road'--and right at the top it says something like "From: EAS Medusa To: Excalubur."
If I remember it right (vaguely recalling an interview in the magazines) either Fiona Avery or one of the other continuity people was responsible for printing off stuff like this, if so then the intent BTS appears to be clear; it's just "Excalibur."
Though the weight of evidence appears to be against the "EAS" prefix, nothing is 100% definitive either way. I suppose what we really need is a quote from JMS or a peek at the Crusade show bible. Perhaps we should bring in Jan for an adjudication?
*rings the Jan bell*