[Dae]

I know that for making most simple solutions you dilute things up to a desired volume with solvent. E.g. a 20% w/v solution of glycine is 20g glycine with diH2O added until the final volume is 100mL. Same story with molarities. But is it the same when diluting concentrated stocks or do you add a specific volume of solvent. For instance if I have a 5X solution of TAE, do I add diH2O to 20mL of 5X stock until the final volume is 1L or do I combine 20mL 5X stock with 980mL diH2O and not worry about the final volume? For concentrated stock solutions the latter makes more sense.

Is there ever a case (besides %w/w) where you add a specific volume of solvent and just take whatever final volume emerges?

Thanks!

[Dae]

For instance if I have a 5X solution of TAE

Please read that as 50X 

[Borek]

As volumes are not additive common approach is to "fill up to" to make sure you know what the final volume is.

The only exception would be v/v solution, where you should mix known volumes of solute and solvent. However, many people have no idea what they are doing and they are preparing v/v solutions starting with v_solute and filling up to v_solute+v_solvent, assuming volumes will add. In most cases it doesn't matter as the difference is small (rarely above 1-2%), but this is incorrect.