Lately, Interstate 6s are made by Trojan. the 225AH one is a T-105 rebranded. The 210AH one is a T-605 (number from memory) The AGM versions are likely Trojans as well--check if their specs are the same.
Interstate site shows one set with black casings marked wholesale only that seem to be the ones Costco shows on their site. Check for same specs as the others.
No idea what is going on there. Need an industrial spy! :)
BTW that DEKA one might be the one with only 190AH. The AGM version of the T-105 has 217AH instead of 225. You get fewer AH with same size in AGM due to the way they are built.