2nd time finding a shade/color difference between old & new batches of Testor's acrylics

I find it more of a problem when buying the bottles at widely different times.  Usually if I buy them at the same time they match, but of course that is still not a guarantee they are from the same branch, depending on when the bottles got loaded into the rack.

I start out with the assumption no two bottles of paint will be exact matches, regardless of identical paint name/brand. If I think a bottle doesn't have enough paint in it to finish a job, I won't even use it for the job. I have poured a nearly empty bottle of the same paint name/brand into another bottle of the same and mixed them together really well before starting, though.