Polikarpov I-16 types 5 and 6?

[GuerraCivil]

I have read that the Polikarpov type 6 was actually type 5 with just open canopy as a standard and that "type 6" would have been a artificial creation by later historians - that we should instead just talk and write about "early type 5" with closed-canopy option and "late type 5" with standard open canopy. Was it actually so in Soviet type spesifications of the time when I-16 types 5/6 were built?

Wiki states that the "type 6" (or "late type 5"?) had some other modifications than just a open canopy as a standard compared to type 5 ("early"):
- a bit more stronger powerplant Shevetsov M-25B with 730 hp compared to Shvetsov M-25 (700 hp) of type 5
- a third Shvak machinegun added to the bottom of fuselage to increase firepower

It would be also interesting to know if some modifications were made on type 5/6 also in battlefield. I have read that in China more firepower was added to some "type 5" planes by installing more machineguns (these mounted over the nose like in the type 10?). It seems also that at least the Chinese considered the type 5/6/10 as three separate types - the type 5 being I-16I, the type 6 being I-16II and the type 10 being I-16III.

When it comes to production, I wonder how many I-16 type 5 and 6 were manufactured - which of these two types/modifications was more numerous and did the "type 6" see any action in Spanish Civil War?