You don't have to mix lye relaxers because the sodium hydroxide in the formula is stable for long periods of time after it was been created. You don't have to mix anything because the sodium hydroxide is already there ready to go.
The active ingredient in most no-lyes, Guanidine hydroxide, is not stable for long after it has been created. So they keep the two chemicals you need to create it (guanidine carbonate and calcium hydroxide) separate until you combine them just before use. Your mixing activates the relaxer by creating the guanidine hydroxide you need which is good for about 24 hours. In No lye relaxers that use Lithium and potassium hydroxide instead of the guanidine hydroxide-- there's no mixing required.
For the last part, there should be some kind of batch number or something on the tub where you can call customer service to verify when the batch was created or something.
