Like any trait in a specialized hobby - a term to describe a valued trait can become overly-defined. Over time, the interest in oxblood has grown as a prized/desired trait. It has gotten to the point where we see many "Is this oxblood?" threads and folks hope that the brown in their marble is indeed what we call oxblood. I think that the interest in oxblood can cause us to over-define it.
Occam's Razor (slightly translated) states that: "Give two otherwise equal solutions, the simpler one is the better." I tend to believe in simpler solutions to what become difficult definitions. To this end I'll pose this question:
"Was that marble with "oxblood" a manufacturer's production item?" Was it in their Salesman's cases? Was it a standard production item?
If the answer is yes, and it meets the conventional definition of oxblood color glass broadly accepted in the collecting hobby - then I would call it an oxblood. I think we tend to lose sight of the fact that a marble factory made marbles that conformed to specific types as ordered by and sold to their retail customers. It wasn't a free-form, "make whatever you want today" manufacturing business. Look at the stock boxes (which is what retailers received and sold from). The marbles in them conformed to a standard. They were products with defined characteristics. The huge marble dumps that contain marbles that didn't conform to the manufacturing established standard for color and appearance are a testament to their quality control to a standard.
I recommend that we focus on the manufacturer's stock box/bag/etc. products and look at oxblood as a standard glass choice. If we focus on the exceptions (and there are huge numbers of exceptions because there have been so many digs at factories - I predict that we will not succeed in agreeing what oxblood is. I could give you my simple definition of oxblood that I use - and a moment later produce a few examples that break at least on the the definition rules - all the while being true oxblood because it is a dug example that came from a problem or experimental run. Exception can cause us to get off track.
These comments are made without addressing the oxblood that came from German hand-gathered marbles. This is a specialty collecting area and I believe that just about everyone who collects them know what is and isn't "oxblood".
We can debate the chemistry - but to what end? No-one is going to develop a litmus test for marbles.
I have a lot of Akro oxblood cullet. There are some mild variances - but they are generally consistent with the definition that has served me well or many years.
I think that any discussion of a marble trait definition has to keep in mind that novices need to be able to grasp it visually (after handling valid examples) and it have relatively simple visual diagnostics that all of us can look at, point to, describe and say "that is oxblood BECAUSE........."
My two cents,
Alan