The law of the third IS an average. It's nothing else. As for your 700,000 spins, you can use them as one continuous data stream, mix them up, reverse them, turn them inside out. It doesn't matter because each outcome is random.

If you were to divide the 700,000 outcomes into intervals of 37, you would get 18,918 complete separate sets. If you counted how many different numbers appeared in each set, added up the total and divided it by 18,918, you would get a figure of approximately 24. On average, in every 37 spin interval, 24 numbers will hit and 13 won't.

Point being, if you went to a casino now and used a well-designed law of the third system, the probability that you will leave in profit is overwhelming.