Study, study, study - you can't do this and have a life, too.  Seriously, it takes time, but it isn't rocket science. There is a lot of GOOD published material - you were just very unlucky. I've never seen that Bowers site before. He may a whiz on some other items, but he does not know squat about Krags. The general serial number ranges are known from prior reasearch, and, sufficient study will pretty well tell you whether a gun is right or wrong. They did not make rifles and carbines at random. So, when you see an "1898 Carbine" in the 400000 range, you immediately KNOW it's bogus.

I guess you could say the whole carbine issue, and why it is important to be able to distinguish one from a rifle, is that they sell for more money, sometimes much more, and are thus more sought after. If demand were equal, no one would care.

On earlier (1896) Krags, you need to know what to look for, and have some idea of the numbering. 1898 Carbines are a problem - we know 5000 were made, from the army records. We know, from existing records that that they occur in a certain general range - but that span is WAY more than 5000 numbers. Now, it gets tricky, because, once separated from their distinctive stock, and having had later-model sights installed they are visually identical to an 1899 Carbine, except for their 1898 date. Since we do not know all the numbers, fakers have taken common 1898-dated receivers within the known span, put genuine carbine barrels on them, and then collected a premium for having a rare model. Genuine 1898 carbines in range, with an original short M1898 carbine stock are considered quite scarce and desirable.

Plain old "Model 1899" carbines are easy to spot, because ALL guns with that marking were originally made as carbines, so, there is nothing to be faked.