I recently bought an Epson "Signature Worthy" paper sample pack for testing. It contains 2 sheets each of various Epson papers, including Hot Press natural and bright, Cold Press natural and bright, Velvet Fine Art, Exhibition Fiber, and Ultra Premium Photo Paper Luster. Previously, I had tested all but the Hot and Cold Press papers. When finished printing the test sheets for those, I decided to see if there was any difference between my prior tests of Velvet Fine Art and the paper in the sample pack, because it would represent a newer batch. The resulting test print was visually shockingly different from my previous test. The blacks were weak compared to the earlier results. What happened? The sample pack papers were all packed with their stickers facing the same direction, with the obvious glossy papers having the stickers on the backs. So, I hadn't checked whether this was also true of the matte papers that were hard to differentiate front from back. In the case of those, however, the stickers were on the front side.
If you get a sample pack that has mixed paper types, and you have some that you can't tell front from back, do the finger lickin' test. Lick the pads of your thumb and forefinger and pinch a corner of the paper. The side that sticks the longest when you pull your thumb and forefinger away is the coated side.
After printing the ink test on the "back" side of the Velvet Fine Art, it now visually matched my previous results. WHEW! But now, I know not to trust Epson to label their own matte papers, and advise you not to assume that the papers are bad if you got one of those signature worthy sample packs and followed your best intuition. Test for the coated side.