Well little of what is here actually answers the question, no offence guys.

It is in fact unlikely that Livy combined different accounts. What Livy is more likely to have done is identified the account that seemed the most right and copied it.

Why?

Because sythesis wasn't used in the ancient world. Remember the written accounts of a historian's predecessers are all he has to go on. If he starts mixing them up then the picture will get even muddier. Suppose he gets it wrong, then he's just making stuff up. Its not that Livy didn't use different sources, he did, he even used some sources to fill holes in others but he never mixed them up, taking them all apart to try and get at the "truth." Thats a very modern concept.

There is plenty of evidence that there were five classes in the Legion, bear in mind that there were free plebs too poor to actually serve in the Legions.