Nice catch! Always wondered why we never saw him in Empire.
Well, as far the lore goes there’s roughly four years between ANH and ESB, so a lot could have happened. He might even have been killed, hence his absence on Hoth. Also, I’m not too sure how the new canon works, so I guess he could simply be somewhere else during that time period.
Is the Rebellion larger in the new EU? That’s the impression I’m getting from a lot of the discussions about it here on the forum. I always figured that the Rebels in the OT, before the PT and Disney was mostly one small army with several smaller branches around the galaxy, but I guess that’s no longer the case?
(PS. I didn’t technically “catch” the above detail, unless you count me watching a YouTube video and sharing a link and a screenshot here as a “catch”.)