I have a durometer and they measured identical so that would be super odd. They would have to be a fundamentally different material.
They used to be slightly different color, stock ones being more yellow-ish orange while aftermarket were bright clean orange. All the sets I’ve seen lately has had those bright orange ones stock.
That would make sense then, that the stock ones are now the same as the after market ones.
Just funny that they had such different bushings, even some of the stock dark red coloured ones were so hard compared to the other ones, but all the rest of the stock bushings - white, black, another colour and of course orange in the stage 11s were all the same when we tested them, cause some people were tripping on the different coloured bushings in all the various versions of the trucks, mainly the different graphic trucks, eg Thrasher versions, Wes Kremer, Luan Olivera, round cross logo, bar logo, etc. So many of them.