I believe the GP's do have date codes on them (will have to check).
I have heard the latest 'batch' are producing very low voltage, but excellent run time.
Yes, there are many different matchers out with and the numbers are all over the place ... different cut off's etc.
You have to remember some of these guys do this for a living and make money from this. Some 'can' play with the numbers (if they wanted). Remember high voltage 'team' packs and regular club packs all go through the same amount of time and energy to arrive at their state. The matcher pays the same amount of money for those 2 different packs, but makes a lot more money on the high voltage pack ... don't you think they want to sell more packs with higher numbers..... hmmmm
I personally run Pole Position Batteries, out of Montreal, Quebec Canada. Great guys, 'real' numbers and if you are from the states, the exchange rate on the US dollar make them that much better.
They do not sell direct, so have your LHS give them a call and order you in a few packs to try. Hey, tell them I sent you
I could be wrong, but I believe Pole Positon has NEVER seen a pack of GP's come off with over 1.15v or 415 seconds of runtime.
And most of them all get their bulk cells from the same places.
If you are not a factory driver and find a pack like 1.159 @ 425s,
I would second guess those numbers...
Our local club have guys using all different matchers cells (SMC, Fantom (which is SMC matched), Trinity, Nuclear, Orion, etc.)
Most of the GP's seem to be around 1.14v and average 400 seconds (all at 30 amps)...
I have also read another thread, where everyone is talking about how short the life cycle is on new cells now a days.
This leads me to think about what the matchers are doing to increase their voltage numbers. They seem to be producing higher voltages, but killing the extended life of the cells.
So yes, they may be great numbers, but chances are they can only last 4-6 months before the voltages drops off the face of the erth....