Ive noticed while playing Grom and the greenskins their is a lot of inconsistency with buffs. The Regiments of Renown variants of the goblins specifically seem to have issues.
The "Deff Creapers" dont seem to benefit from anything but tech upgrades. Perhaps red lord skills too I didnt have them on my lord in the last greenskins campaign. Lava spider riders aren't getting the goblintide buff, or the ammo upgrades from the Flyin Gubbinz section. Neither is the "Deff Creapers". "Da Rusty Arrers" ARE getting the infantry buffs from troll meat and buffs from other cauldron meals. Spiky skin and physical resistance. I can't seem to find any word if this is intentional. Lava spider riders already have decent armor pen and are extremely cheap units, almost free, but the "Deff Creapers" are like 40% more expensive than spider rider archers and only really have decent leadership and stalk to compansate. One ammo upgrade immidiaetley makes vanilla riders WAY more effective. There is no doubt more stuff I'm missing but the goblin tide and ammo upgrades are the biggest deal here.