The LEGO pieces in the bags look legit, but wondered why the bags are different. The box appeared to have been opened when I received. Just want to make sure the bags are official LEGO before I try to sell. The bags have "LEGO Group" written on them, so that's positive.
First of all, congratulations on securing a 75054 AT-AT. This is a very desirable set, and costs a pretty penny to purchase now that LEGO has stopped producing the set.
There is nothing wrong with your bags. The bags with the white band are of a newer design than the bag labeled "4". The white-band style was introduced in 2015, whereas the older style was used as of 2011. LEGO is slowly phasing out the older style in favor of the white-band style, working through remaining supplies of the latter until they run out.