Bit of a pity the industry standard for so many years has gone off the boil with quality. Sign of the times I suppose. Still have a tin of Extracolour Satin which still works after 20 odd years.
For dead flat I now use either Testors dullcoat, when I can find it, or the SMS brand of flat which is an acrylic laquer. I have had a couple of occasions where the SMS went a bit whitish, probably due to humidity, but a light over spray of Laquer thinner fixed that up.
For pure acrylic, Gunze still works most of the time... with the priviso of the above, if you get the whitish haze, an over spray will generally fix it.