I feel like this has devolved into people just telling to switch to 2.0 instead of address the question I asked. That's all good and well but the question hasn't been addressed at all.

You cannot retrieve the transaction subtype purely from the transaction id

Well, you could try a search or lookup to get the type:  

var transType = nlapiLookupField('transaction', transid, ['type']).type;

@scottvonduhn understood. Thank you for the reply btw. This is really helpful.