I wonder if the OP has considered cleaning his old slabs, perhaps so they are a better match for the new (clean ?) slab
And what I'm saying is, it depends on just how far that mismatch goes. Hence me citing my 'taking to its logical conclusion', which you so cruelly dismissed... Hey-ho - let's await the piccies
just two mismatched slabs, just two - I wonder which Judge is going to waste their time with that one ? Judge Judy, Judge Dredd, Judge Jules ?